In Moscow, Patriarch of Moscow and All Russia, Aleksy II, celebrated a midnight Mass for 5,000 people at Christ the Savior Cathedral.
The five-hour service was broadcast on national television.
Orthodox Christmas was not officially recognized by the communist regime, but became a public holiday in Russia following the collapse of the Soviet Union in 1991. Communists demolished thousands of churches, including Christ the Savior Cathedral, which was rebuilt in the late 1990s.
The Greek Orthodox patriarch of Jerusalem, Theophilos III, began Christmas ceremonies for Greek, Syrian, and Coptic churches at the ancient Church of the Nativity in Bethlehem on January 6.
The rites were attended by locals and tourists, but in lower numbers than in previous years.
Security concerns contributed to a drop in tourist numbers. The town is cut off from neighboring Jerusalem by Israel's security barrier. People are also concerned about internecine violence that has peaked in recent days in Palestinian areas.
Kosovo's Last Christmas?
Meanwhile, Orthodox Serbs in Kosovo celebrated Christmas in the shadow of an imminent UN decision on the fate of the breakaway Serbian province, where the Albanian majority demands independence.
Kosovo's remaining 100,000 ethnic Serbs are looking to the future with uncertainty.
"I can't say it'll be the last Christmas in Kosovo, because I'm an optimist and I believe there will be even more in Kosovo," Slavisa Stefanovic, who lives in Kosovska Mitrovica, told Reuters television. "No offence to anyone, but Christmas is always most beautiful in Kosovo."
Father Milija Arsic from the St. Dimitrije church on Miner's Hill above Mitrovica, told Reuters that Serbs will remain in Kosovo.
"We know we are on our own ground, and we will try to stay," Arsic said. "Here was the Serb state, and if God wants it will remain so."
Christmas celebrations in Russia were marred by news of the murder of an Orthodox priest.
Interfax reported that the priest was murdered; religious icons stolen, and his church burned down on January 6 in a village near the Ural Mountains. Twenty-one religious icons, some over 100 years old, are missing from the church. The news agency reported that several suspects had been detained.