Acute toxicity of phoxim, acephate, isofenphos-methyl and isocarbophos on male SD rats of clean grade was carried out by gastric lavage method at room temperature of 18℃. These rats are 4 to 5 months old with body weight of 180 to 220 kg. The results indicate that the orders of the toxicity of these four pesticides on SD rats are isofenphos-methyl, isocarbophos, acephate, phoxim. We found that the median lethal concentration of phoxim in 24 h, 48 h, 72 h and 96 h is 3.892g/kg, 3.051 g/kg, 2.618 g/kg and 2.458g/kg respectively; the median lethal concentration of isofenphos-methyl in 24 h, 48 h, 72 h and 96 h is 0.015g/kg, 0.013g/kg, 0.012g/kg and 0.011 g/kg respectively; the median lethal concentration of isocarbophos in 24 h, 48 h, 72 h and 96 h is 0.049 g/kg, 0.046 g/kg, 0.043 g/kg, 0.041 g/kg respectively; and the median lethal concentration of acephate in 24 h, 48 h, 72 h and 96 h is 0.137 g/kg,0.113 g/kg, 0.100 g/kg,0.085 g/kg respectively. Finally, we evaluated the characteristics of toxicity effect and safe concentration of these pesticides to SD rats.