Abstract: In order to study toxic effect of fenvalerate (FEN) on Odontobutis potamophila juveniles, static bioassays were conducted. Results show that the 24, 48, 72 and 96 h（t） ρ（LC₅₀）of FEN to the fish with 95% confidence interval was estimated to be (3.19±1.38), (1.66±1.02), (0.98±0.69) and (0.70±0.49) μg•L^-1, respectively, with the safe concentration being (0.13±0.97) μg•L^-1. LC₅₀ of FEN decreased significantly with time, which fits an exponential decay model: ρ(LC₅₀) = 0.915 1+15.012 3×exp（-0.075 8×t） (r=0.9962). LT₅₀ decreased significantly with FEN concentration ρ(FEN), which fits the model t（LT₅₀）= 2 653.467 6×exp-5.590 4×ρ(FEN)+ 56.378 7×exp-0.209 5×ρ(FEN) with r = 0.999 4. CAT and SOD activities and MDA content in liver of the fish varied significantly with time and FEN concentration (P＜0.05). Interactions between the two factors were not so significant. SOD and CAT activities peaked in Group 4 μg•L^-1 after 24 h and then declined. MDA remained almost unchanged in all the groups after 24 h of exposure, and rose significantly in Groups 4, 6 and 10 μg•L^-1 after 48 and 96 h (P＜0.05). Two way ANOVA shows that interactions between the two factors, time and concentration, affected Na⁺/K⁺-ATPase activity in gill of the fish significantly (P<0.05), and the activity decreased significantly in Groups 6 and 10 μg•L^-1 after 24, 48, and 96 h of exposure. The above-discussed indices may be used as indicators in evaluating toxic effect of FEN. Through pathological observation, it was found that FEN pollution caused serious damages to gills and livers of the fish: gill disorder, epithelial cell proliferation; columnar cell rapture, hepetocyte vacuolation, bile duct endothelial cells hypertrophy and mergence.