Abstract: Caohai, lying on the eastern Yunnan and Guizhou Plateau, is the most important wintering and stopover area for waterbirds in the southwestern China. To document species, their populations, and changes of waterbirds wintering at Caohai, a survey was conducted on 11-12 January 2012. Twenty-six species of waterbirds, with a total of 76,872 individuals were recorded. Of the 26 species of waterbirds, 8 species had a population of more than 1,000, including Common Teal (Anas crecca), Black-necked Crane (Grus nigricollis), Spot-billed Duck (Anas poecilorhyncha), Bar-headed Goose (Anser indicus), Tufted Duck (Aythya fuligula), Ruddy Shelduck (Tadorna ferruginea), Eurasian Wigeon (Anas penelope), and Coot (Fulica atra). Coot, Eurasian Wigeon, and Ruddy Shelducks each had population of near 10,000 or more. Over the past 20 years, the total counts of waterbirds have been between 50,000-80,000. Numbers of Black-necked Cranes have been increasing steadily, while Eurasian Cranes (Grus grus) have been declining. The number of diving ducks is far less than the number of 10,000 diving ducks in 1996, likely due to the decline in water quality at Caohai over the past decades. We recommended the following measures be taken into account in waterbird monitoring and protection: more systematic waterbird count; special attention paid to species or groups with dramatic increase or decrease; land use and change to be monitored; and urgent measures to be taken on pollution, invasive species, urban expansion, and tourists.