The meeting between the seven permanent and five non-permanent bishops of the Holy Synod is taking place at the patriarch's residence in Peredelkino, outside Moscow.
Church spokesman Father Vladimir Vigilyansky earlier told RIA Novosti that as well as electing an interim leader, the Synod would finalize details on the funeral and requiem service.
Alexy II, the Patriarch of Moscow and all Russia, who led the Russian Church for 18 years, died at the age of 79 in his residency near the capital on Friday morning.
He will be buried on Tuesday in the Annunciation side-chapel of Moscow's Epiphany Cathedral, Vigilyansky said.
The patriarch's body is to be brought to the Cathedral of Christ the Savior later on Saturday, where it will lie in state through the night.
A senior church official said earlier that heart failure was believed to be the cause of death. The patriarch was known to have suffered from health problems in recent years.
Alexy II became patriarch of the Russian Orthodox Church in 1990, shortly before the collapse of the atheist Soviet Union, and presided over a religious revival in Russia, with thousands of churches and monasteries being restored and hundreds of new ones built across the country.