The following is a timeline of the Syrian civil war from May to December 2013. Information about aggregated casualty counts is found at Casualties of the Syrian Civil War.

May 2013 1 May The Russian Federal Air Transport Agency ordered civilian flights to cease flying over Syrian airspace.

2 May Alleged Bayda and Baniyas massacres commenced; according to a later U.N. report, between 300 and 450 civilians were killed in the two massacres by Syrian forces.

3 May An attack in Rif Dimashq Governorate, when allegedly IAF bombed a suspected weapons site.

4 May Rebels continued their siege on Meng airbase. It was claimed that rebels had killed the base commander in clashes, and also seized the second military detachment of the base. Rebels claimed that a group of pilots defected and assassinated the base's commanding officer. The defected pilots told rebels that around 200 soldiers remained in the base, garrisoned in the headquarters building supported by a handful of tanks. Many soldiers resorted to sleeping under tanks, fearing a rebel assault.

5 May Planes, reportedly of Israeli origin, hit targets just outside Damascus.

8 May The Syrian government is reported to have blacked out all internet traffic into and out of Syria. Syria "has largely disappeared from the Internet". A similar event took place in November of last year.

Syrian Internet services were restored after a 19-hour blackout.

9 May The Philippines is strongly considering withdrawing its 342 peacekeepers stationed in the Golan Heights after four of its peacekeepers were kidnapped by rebel forces.

10 May 3 Lebanese nationals were killed in fighting in Syria, a further 36 have been reported missing. How they were killed and whom they were fighting for remains unclear.

Rebel fighters managed to cut off the strategic road to Halab al-Jadida, that was the main supply line for the Syrian army between Hama and Aleppo. This happened through taking over the 2 checkpoints of al-Qebtein and Um Amud.

11 May Rebels managed to cut a newly build desert road used as an Army supply route between central Syria and Aleppo's airport.

12 May The Syrian army took control of Khirbet Ghazaleh, Daraa.

An explosion in the Syrian-Turkish border town of Reyhanli killed 46 and wounded 155 Turkish citizens.

13 May The Syrian army captured the towns of Western Dumayna, Haidariyeh and Esh al-Warwar, near Qusayr.

A Turkish F-16 on an operational mission crashed near the border with Syria. Locals in the village of Yarpuz on the Turkish side of the border reported a loud explosion.

15 May The United Nations updated their estimated death toll of the entire conflict to 80,000.

The United Nations General Assembly passed a resolution (GA/11372) adopting a "Text Condemning Violence in Syria, Demanding That All Sides End Hostilities". The resolution passed the General Assembly by a vote of 107 in favor to 12 against, with 59 abstentions.

The twelve countries voting against the resolution were Belarus, Bolivia, China, Cuba, Democratic People’s Republic of Korea, Ecuador, Iran, Nicaragua, Russian Federation, Syria, Venezuela and Zimbabwe. Most of these countries, known in some circles as the "Gang of Twelve", are noteworthy for their current or past Communist or Communist influenced governments (in the case of Belarus, China, Cuba, North Korea, Nicaragua, Russia and Venezuela) and/or record of human rights violations (as in the case of Iran, Syria and Zimbabwe).

There has been, apparently, a conscious effort to suppress information regarding this resolution as it is difficult to find information concerning it on the Internet.

16 May The Syrian army repelled a large rebel assault on an Aleppo prison. The attack was aimed at dislodging government forces and freeing an estimated 4,000 political prisoners are being held there, however the rebels were forced to retreat after airstrikes caused casualties among their ranks. Rebels blew open the prison's main-gate, and took control of a building.

Rebels besieged the 52 Brigade in Daraa. Rebels also claimed they recaptured the town of Qaysa, Rif Damascus, after launching a unified counter-offensive. Rebels also launched an attack on the Brigade 52 base in Daraa province.

By the end of the day 110 people were reported killed by the Syrian army with 60 were reported killed in Damascus and its suburbs.

17 May The Russian navy has expanded their use of their naval base at the Syrian port of Tartus. Previously Russian ships only periodically visited the port, however in the last three months an average 10-15 ships have been reported as having been positioned near the port "at all times".

Rebels captured four villages in Eastern Hama, including the Alawite town of Tulaysiah. The villages were abandoned by its residents days before the rebels arrived.

The Human Rights Watch released a report about the government's mass-torture centers in Raqqa, which were previously accessible until Rebels captured the city.

18 May Rebels took control of the villages of al-Tleysiya, al-Zughba, al-She'ta and Balil in East Hama.

The father of Deputy Foreign Minister Faisal Mekdad has been kidnapped, based on past tactics, by rebel forces his home in Ghossom. In the Syrian-Lebanese border town of Qusayr rebels claimed to have killed at least 10 Hezbollah fighters in an ambush.

19 May Heavy fighting is reported in Qusayr, Syria, as the Syrian army launches a major offensive against rebel forces.

20 May Deliberate gunfire from the Syrian-controlled side of the Golan Heights struck an Israeli patrol vehicle, Israeli soldiers returned fire, destroying the Syrian fire position.

Elite Hezbollah reinforcements were sent from Lebanon across the border to al-Qusayr. Activists reported that much of the town had been destroyed by this point.

22 May US Senate panel backs arming Syrian rebels.

In fighting at Nayrab rebels have seized an army base and several army checkpoints, killing 40 Syrian soldiers and pro-government militiamen in the process with the loss of 14 rebels.

23 May A former government scientist claims that the Syrian government is using diluted chemical weapons, such as with alcohol, on rebels to slow their advance while reducing the number of casualties, leaving open the question as to whether it was military grade tear gas or nerve gas that was used in these attacks thus avoiding the U.S. "red line" on chemical weapons. Amongst the areas were the weapon were alleged to be used are certain suburbs of Damascus, Aleppo’s Sheikh Maksoud district, Saraqeb and Homs. The scientist, who worked for Centre for Scientific Studies and Research, claims that the alleged gas attack on Khan al-Assa, Aleppo, on 19 March 2013, was likely tear gas and not nerve gas.

26 May On 26 May 2013, two rockets hit a Hezbollah area of Beirut injuring five people whilst another two rockets caused property damage to buildings in the al-Hermel district of Beirut. Syrian rebels have been blamed for the attack as they had promised to attack Hezbollah targets in Lebanon in retaliation for their helping the Syrian army particularly in the border town of Al-Qusayr. Syrian rebels have also shelled al-Hermel previously.

27 May Fighting between Kurdish (YPG/PYD) and Liwa al-Tawhid forces in the Ras al-Ayn village near the border with Turkey left 11 dead and 20 wounded.

The United Nations Relief and Works Agency for Palestine Refugees (UNRWA) reports a large explosion in Sbeineh Camp, Damascus Governorate, on 27 May 2013. Early reports suggested that the explosion was caused by a ground-to-ground missile or airstrike. The attack claimed the lives of at least five Palestine refugees. A further eight were wounded and dozens of refugee homes were reportedly destroyed.

28 May LCC reports 112 people were killed by the end of the day. 35 were killed in the Damascus suburbs.

29 May LCC reported 161 people killed that day, including 12 women, 8 children, and 5 under torture. 53 were killed in the Latakia province.

30 May A Syrian army general in March asked Rosoboronexport for a quote on a large number of military items "in the shortest possible time." These items included 20,000 Ak-47s, night vision equipment, 40 mm grenade launchers and some 15,000,000 rounds of AK-47 ammunition. In relation to arms sales to the Assad government Deputy Foreign Minister Sergei Ryabkov stated that Russian arms, such as the S-300 surface-to-air missile, may actually "help restrain some 'hotheads' considering a scenario to give an international dimension to this conflict,"

31 May The Syrian army attacked a convoy trying to remove injured people from the town (according to activists), killing at least 7. Local people report that 15,000 civilians remained trapped in the town with food and water running low. Civilians had to wait 3–4 days for drinking water.

LCC reports of 163 people killed by the Syrian army, including 66 in Aleppo, mostly in a prison massacre.

June 2013 12 June At least 14 killed in double suicide attack in Damascus. Syrian helicopter fires on Lebanese town of Arsal.

14 June US Government confirms that government forces used chemical weapons in Syria killing up to 150 people and announces increased "military support" to rebels as well as considering a limited no fly zone.

23 June The Syrian Army captured the rebel stronghold town of Talkalakh. Following the assault, 39 local leaders of the Free Syrian Army surrendered and handed over their weapons. The Syrian opposition denied the town had fallen and claimed there was still fighting ongoing however reporters on the ground said there was no sign of it.

July 2013 5 July On 5 July 2013, an explosion occurred in Latakia port city either as an alleged result of an Israel Defense Forces strike against targets believed to contain Yakhont anti-ship cruise missiles supplied to the Syrian government of Bashar al-Assad by Russia,"Israel targeted Russian-made missiles in Syria, US officials say". The Guardian. 14 July 2013. or a result of mortar fire exchanges in the area. CNN reported that the strike was carried out by the Israeli Air Force, while the Sunday Times reported that the explosions were the result of a cruise missile fired from a Dolphin-class submarine."Israeli submarine strike hit Syrian arms depot". The Jerusalem Post. 14 July 2013. The blasts occurred at a military complex in the town of Samiyah, near Latakia."The explosions in Latakia: Before and after". Israel Defense. 13 July 2013. On 13 July 2013, United States officials said that Israel carried out an air attack that targeted advanced anti-ship cruise missiles sold to the Syrian government by Russia. Their conclusion was based on intelligence reports."Israel Airstrike Targeted Advanced Missiles That Russia Sold to Syria, U.S. Says", New York Times. 14 July 2013 The FSA speculated that "enemy aircraft" were responsible, while Hezbollah's Al-Manar claimed that the explosions were caused by "stray mortars" from "local clashes." Israeli media later reported that the attack had been carried out by cruise missiles launched from a submarine.

11 July Abu Bassir Al Ladkani, a top commander of the Free Syrian Army (FSA), was assassinated. The assassination was carried out by al Qaeda-linked militants.

August 2013 3–5 August Islamist rebels kill at least 200 people during a three-day assault on Alawite villages in Latakia province. According to a local cleric, at least 100 of the victims were civilians, most of them women and children. A catholic nun said that the number of civilian casualties could be as high as 400-500 and many of them were mutilated, beheaded or dismembered alive. Also, kidnapping of other 150 civilians has been reported.

6 August