The acute toxicity of glutaraldehyde, dibromohydantoin, methionine iodine and bleaching powder to juvenile Pinctada maxima was studied. The results showed that the order of toxicity was bleaching powder>dibromohydantoin>m ethionine iodine>glutaraldehyde and the median lethal concentrations (LC50) of above disinfectants were 13.05 mg/L, 27.49 mg/L, 53.20 mg/L and 67.36 mg/L, respectively in 24 h and the LC50 were 10.15 mg/L, 9.35 mg/L, 29.27 mg/L and 35.58 mg/L respectively in 48 h; and their SC (safe concentration) were 1.86 mg/L, 0.32 mg/L, 2.66 mg/L and 7.52 mg/L respectively. The research indicated that we can use glutaraldehyde to disinfect P. maxima under safe concentration, but should not use bleaching powder, and can use dibromohydantoin and methionine iodine carefully. Based on the results of the pre-experiment, the LC0 and LC100 treated by dibromohydantoinm were 3.0 mg/L and 94.0 mg/L, respectively. Five mass concentration of dibromohydantoinm were determined according to the two mass concentrations above by equal spacing method, the results of the test of the toxicity of dibromohydantoinm to the larvae of P. maxima were shown in Table 2.