To explore the toxicity of trimethyltin chloride (TMT) on fish, effects of TMT on physiological and biochemistrical characteristics of Danio rerio were measured using the acute toxicity test. According to the 96 h-LC50 value of TMT, three different concentration groups (0.39, 0.78, 1.17 mg·L-1) were set. The activity changes of Na+,K+-ATPase in the gills, AchE in the head and SOD in the muscle were detected in 72 hours. The results showed that 96 h-LC50 value of TMT on Danio rerio was 2.35 mg·L-1 and the safe concentration was 0.23 mg·L-1. There was a significant inhibition to Na+,K+-ATPase in the gills. When TMT concentration was more than 0.78 mg·L-1, the enzyme activity was virtually inhibited (the inhibition ratio>32%). Na+,K+-ATPase activity was inhibited in the low concentration (0.39 mg·L-1) and had a trend of recovery to the level of control group after 24 h. TMT showed an inhibitor to AchE in the head of Danio rerio, which would increased with the increasing of the time and medicine density. Because of the high motion of AchE in the head, only Danio rerio in the most concentration group (1.17 mg·L-1) was significantly inhibited (p<0.05). SOD activity in muscle of Danio rerio showed that the trend of increasing first, and then decreased. The higher TMT concentration was, the faster the enzyme activity activated and declined. Among all groups, the groups of 0.39, 0.78 and 1.17 mg·L-1 would get to the most inhibition effect which were 153%, 145% and 153% times of control group at 48, 24 and 12 h, respectively. All results indicated that TMT was high toxicity to Danio rerio. Na+,K+-ATPase in the gills was the important target of TMT.