This study deals with the toxic effects and the safe concentrations of Methamidophos, Benthiocarb, Dinitramine and Benzimidazolyl-methyl ester and the subacute toxic effects of Methamidophos on Macrobrachium rosenbergii. The median lethal concentrations and the safe concentratins of these four pesticides on M. rosenbergii were determined. The order of the toxicity of these four pesticides was obtained, that is: Methamidophos >Benthiocarb >Dinitramine >Benzimidazolyl-methyl ester. The juveniles had been cultured in 7 groups containing different concentrations of Methamidophos for 15 days to determine the subacute toxic effects of Methamidophos on juveniles. The growing speed in the experimental groups is lower than the control group,and the higher the concentration is, the lower the speed is.