I thought of visiting Beijing around December 2012, is it suitbale (weather)? Its a 5D4N visit.

Generally speaking, december in this city is a cold month, with average high temperature at about 3C and low temperature at about -5C. It will be dry at that time with few snow. But the exact climate of this year is hard to say, so I advise you to keep notice on the climate when you come.