Cambodia in December is characterised by dry, sunny weather, low humidity and relatively cool temperatures (avg temp: 26 °C) throughout the country. It's no surprise that December is amongst the most popular months to travel to Cambodia. If you do see rain it would be unusual.
It's good news across the country with dry conditions and pleasant temperatures expected across Cambodia. Long days of touring the Angkor temples are very achievable with extremely high temperatures still being a number of months off. If you're looking for a Christmas getaway in Asia, look no further!
On the main waterways of the Tonle Sap & Mekong River, the levels are still fairly high, making visits to the floating villages by boat still possible. In the eastern and western provinces there is still plenty of colour and the ground is fertile. Something that will change soon enough...
To the south, the mainland beaches and nearby islands are well primed for R&R time. For the more adventurous, there are favourable diving conditions in the waters surrounding Koh Rong and Koh Rong Samloem.