Abstract: Effects of prenatal exposure of three organophosphorus pesticides on neonatal brain structure in mice were investigated.2 mg/kg bw of diazinon,2 mg/kg bw of chlorpyrifos and 50 mg/kg bw of acephate were injected subcutaneously daily during gestation days 7.5-11.5 of ICR mice.Quantitative morphology in hippocampus and somatosensory cortex were measured.The results showed that diazinon and chlorpyrifos caused glia number in somatosensory cortex reduced by 14.29% and 21.43%,respectively,and chlorpyrifos caused the ratio of glia and neuron reduced by 24.19%.The number of pyramidal cell in hippocampus CA1 decreased by 9.30％ and 20.93％ after treatment of diazinon and chlorpyrifos,respectively,and the volumn density of pyramidal cell decreased by 27.05％ after treatment of chlorpyrifos.Meanwhile,the number of pyramidal cell number in hippocampus CA3 decreased by 22.22％ and 19.44％,and the volumn density of pyramidal cell decreased by 23.54％ and 18.98％ after treatment of diazinon and chlorpyrifos,respectively.Acephate had no significant effect on somatosensory cortex and hippocampus.