Pesticides causing damages to the erythrocyte nucleus of loach, Misgurnus anguillicaudatus Cantor, were reported in this paper. On the basis of determining 96hr LC50of methamidophos, the effects of two pesticides on micronuclei and nuclear anomalies in erythrocytes of loach at five different concentration between LC50 and the safety were discussed. The experimental results indicated that the two pesticides could increase the frequency of micronucleated erythrocytes and the rate of nuclear anomalies. At the certain range of the pesticide concentration, the frequency of micronucleated erythrocytes showed a dosedependent elevation. However, it decreased with the increase of pestcide concentration when the concentration was over a suitable range. But the rate of total nuclear anomalies showed a significant dose-dependent increases in the test. In addition, with the increase of the doses for each pesticide, the hight frequency of micronucleated erythrocytes appeared also earlier.