We are planning a one day trip from Rome to Florence on Dec 24th.
Could if questions here.
1. Does everything is going to be open on a Christmas eve?
2. Should we book it in advance ($130 round trip from www.raileurope.com) or we can just buy tickets from the train station on 24th)?
3. What we should not miss spending just one day in Florence?

Not sure about the hours on Christmas Eve for Florence attractions. Hours may be reduced, or things may be closed. I'd check the websites of places you're thinking of visiting first.

I'm especially partial to the art museums in Florence, if they're open that day. Depending on your interests, choose from the Uffizi, Accademia, Pitti Palace, or Il Bargello. You may want to make reservations online ahead of time at some of these.

A search of attractions lists for Florence at the Frommer's or Fodor's websites should give you plenty of ideas.

You are going for a one day roundtrip from Rome to Florence and back on Christmas Eve? And you want to see the highlights of Florence?

Sorry to be negative, but I think you will miss a very important day while travelling and scrambling--stay in Rome and enjoy the day and Christmas in Italy!

I would think many things would close early on Christmas Eve - and this is probably one of the busiest travel days of the year - so getting advance tickets makes sense - after you check to see what's open.

Plus Christmas Eve falls on a Friday, which would make travel even more crowded.

Wouldn't there be some Christmas Eve services? Are the churches decorated in a special way? There was a particular church that I wanted to see (I think it was San Lorenzo) and the only way I could see it was by attending mass. It was a great way to see the church.

"Wouldn't there be some Christmas Eve services?"

Sure--Midnight Mass....and then return to Rome via a train--absurd! Especially when you have left Rome with all its culture, Christmas traditions and if you want--Midnight Mass! The more I think about this plan, the more it sounds like a bad idea. I repeat--stay in Rome.

macanimals, I am not a Catholic, so, I did not plan to visit Mass anyway. Thank you all; I already made a reservation.

I'm not Catholic either, but attending Mass was the only way to get into the church at the particular time that we in the area. Here's a link with information about the church that suggests that might be open during the day, even on Christmas Eve.
http://www.florence-by-divino.com/ba..._florence.html

I'm not necessarily advocating that you go to Florence or to this church, but I'm also not convinced that it's necessarily a total loss of a day.