A representative of the CIS executive committee, Tatsyana Mikhalevich, said the decision was made at the request of Russia and Kazakhstan.
Russia's Interfax-Zapad news agency in turn quotes an unidentified Belarusian Foreign Ministry official as saying the summit will take place on November 28.
The official said CIS foreign ministers would meet in Minsk on Monday October 16 as scheduled.
The Kremlin confirmed the CIS presidential summit had been postponed, but gave no reason.
Strained ties with Georgia and a bitter dispute with Belarus over gas prices are cited by observers as possible reasons for Russia's decision to postpone the gathering.
Belarusian President Alyaksandr Lukashenka on October 7 criticized unspecified countries he said "consider themselves as first-rank states" for seeking to hold the summit at a later date.