They are not alone in this: other countries who cling to the old tradition include Georgia, Kosovo, Moldova, Montenegro, Russia and Ukraine.
Following the afternoon services at St. Sava cathedral in Belgrade, the oak log - an item used in the Christmas rituals, and known in Serbian as badnjak - will be added to a bonfire in front of the church.
The ritual will also take place in front of other churches, while badnjak branches can also be found in households on this day.
Holy midnight liturgies will be served at midnight on Wednesday, celebrating the birth of Jesus Christ. Those worshippers who observed the four-week period of Lent will also be able to take communion.
The Serbian Metropolitan Amfilohije issued his Christmas message on Tuesday, encouraging the Serbian people to "safeguard the Orthodox faith, language and alphabet established in the time of Cyril and Methodius, and enlightenment of St. Sava, on whichever continent they might live".
"This Christmas season we are especially filled with sadness that our great Patriarch Pavle has left us. We deeply believe that he continues to offer his prayers for our Church and our crucified people," his message read.
In Macedonia, celebrations began on 5 January, the evening known as "kolede", in which neighbourhoods gather together to light a bonfire, listen to traditional music and share food and drink. On 6 January, children go from door to door, chanting the traditional ''kolede'' childrens' song, asking residents for the customary treats of walnuts, fruit and candy. Wednesday, is the Christmas Eve, when the traditional oak log - badnik - is brought to the family hearth.
The house is decorated with oak branches with their leaves, representing the wish of the family for a long and healthy life, "with health strong as oak, and with a life long as that of the oak."
Then the fasting supper, strictly vegetarian, is served.
Bulgaria, along with Romania and Greece moved their time for Christmas observance to 25 December. A recent suggestion within the Orthodox Church to reinstate the "old calendar" dates was rejected by Bulgaria’s Holy Synod.
Both communities in Kosovo blame politics for the trial of Fatmir Limaj - though from diametrically opposing points of view.