United Nations Security Council Resolution 166, adopted on October 25, 1961, after examining the application of the Mongolian People's Republic for membership in the United Nations the Council recommended to the General Assembly that the Mongolian People's Republic be admitted.
Resolution 166 was approved by nine votes to none, with one abstention from the United States. The Republic of China spoke at the meeting but did not participate in voting (did not vote for, against, or abstain).
See also History of Mongolia List of United Nations Security Council Resolutions 101 to 200 (1953–1965)
References
External links Text of the Resolution at undocs.org
https://history.state.gov/historicaldocuments/frus1961-63v25/d178
Texto de la resolución en UN.org (PDF)