Abstract: In order to document the data as a baseline for future study on environmental impact of the Three Gorges Project on the fishes,seasonal variation in haematological parameters of Mystus macropterus and Pelteobagrus vachelli were investigated as well as the difference between the two species in this study. From September,2002 to June, 2003, 111 Mystus macropterus and 124 Pelteobagrus vachelli were collected in Spring, Summer, Autumn and Winter in the Jialing River between Shuitu Town and Ciqikou. Red blood cells, haemoglobin contents, mean cellular haemoglobin contents, serum glucose concentrations,serum triglyceride concentrations, and serum total protein concentrations in the two species were measured. The results indicated that there were significant differences in each haematological parameter among seasons in either of the two species and these haematological parameters did not increase with water temperature. Serum triglyceride concentration in either of the two species decreased significantly in spawning season, Both serum glucose concentration and serum triglyceride concentration was significantly different between the two species. Serum glucose concentration and serum triglyceride concentration in Pelteobagrus vachelli were significantly higher than those in Mystus macropterus in each season.