Preliminary studies on the community structure of planktonic Protozoa across the outlet of Lake Dongting were conducted during May 1995 to January 1997. Protozoa were collected at five sampling stations (one in the Chang Jiang River and four in the lake) once every two months. A total of 145 species of Protozoa was identified, including 34 Mastigophora, 46 Sarcodina and 65 Ciliata. There were 59 species found in both the lake and the river; 27 species found only in the river, and as many as 59 species only in the lake. Of the 145 species, there were 13 new records for China. The total protozoan density varied between 5830-34790 ind. L-1. Generally, at each sampling station, the highest density peak was observed in autumn, while the lowest was in winter.