Abstract: Through the linear regression method and the probability unit method, the salinity（S）and alkalinity（ALK）to the acute toxic effects on Pseudobagras ussuriensis were studied, and by using the Marking joint index evaluation method together, the joint toxic effects were also evaluated. The acute toxicity tests show that the half death concentrations（LC₅₀）in 24 h, 48 h, 96 h of salinity to Pseudobagras ussuriensis were 12.51, 11.57, 9.81‰, respectively, and its security concentration was 2.97‰, while the half death concentrations （LC₅₀）in 24 h, 48 h, 96 h of alkalinity to Pseudobagras ussuriensis were 32.10, 24.37, 13.76 mmol/L, respectively, and its security concentration was 4.21 mmol/L. The joint toxicity results in different period show that both the salinity and alkalinity play certain antagonist roles to Pseudobagras ussuriensis.

Key words: Pseudobagras ussuriensis, salinity, alkalinity, acute toxicity, joint toxicity