When the russian empire went from the julian to the gregorian calendar in 1918, the church did not recognise the change, they did not move the christmas, so christmas day in Russia still falls on the 7. of January (wich would've been 25. of December in the julian calendar).
Also, new year is celebrated just as much, or even more than christmas, wich stems from the communist era, when the state was officialy atheistic, and very critical of religion.