The Baghdad celebration - part of which was broadcast live on Iraqi national television - was led by the patriach of Babylon and head of the Chaldean Catholic Church, Emmanuel III Delly.
He led prayers for "peace in Iraq and in the world" at the Church of the Virgin Mary in the capital's Karrada Christian district.
Christians are about three percent of Iraq's population, but many have left the country over the past few years, fearing the growth of Islamist militancy.
Prayers were offered in Syriac while carols were sung in Arabic.