String Quartet No. 9 may refer to:
String Quartet No. 9 (Beethoven) by Ludwig van Beethoven String Quartet No. 9 (Diamond) by David Diamond String Quartet No. 9 (Dvořák) by Antonín Dvořák String Quartet No. 9 (Hill) by Alfred Hill String Quartet No. 9 (Maconchy) by Elizabeth Maconchy String Quartet No. 9 (Milhaud), Op. 140, by Darius Milhaud String Quartet No. 9 (Mozart) by Wolfgang Amadeus Mozart String Quartet No. 9 (Porter) by Quincy Porter String Quartet No. 9 (Rihm) by Wolfgang Rihm String Quartet No. 9 (Schubert) by Franz Schubert String Quartet No. 9 (Shostakovich) by Dmitri Shostakovich String Quartet No. 9 (Simpson) by Robert Simpson String Quartet No. 9 (Spohr) by Louis Spohr String Quartet No. 9 (Villa-Lobos) by Heitor Villa-Lobos