Abstract: Quantitative protozoan samples were taken monthly by the author at station Ⅱ in Lake Donghu, Wuhan, from March 1981 to April 1982. Results including species composition, seasonal variations and diversity index were compared with those from the same station of this Lake in 1962. The average density of the Protozoa increased annually by 294 individuals per liter. Thus, the protozoan density has increased ca. 2.3 times at station Ⅱ since 1962, and such increase was found to have a close correlation with the increase of algae and bacteria. With reference to the pattern of seasonal fluctuation of the Protozoa, two annual peaks, one in spiring and the other in autumn, as that in 1962 were still observed. However, in 1982, the spring peak occurred earlier and the autumn one lasted longer. Moreover, peaks were much higher than previous decades and the species composition and the dominant species were entirely changed.From the above-mentioned changes and the analysis of diversity indices, the author is of the opinion that the eutrophication of Lake Donghu is still developing around station Ⅱ and showing an expanding tendency toward the area of open water.