Changes in cholinesterase (ChE) activity, electrophoretic pattern of ChE and histopathologic state on the mice serum, brain and liver by administration of organophos-phorous insecticides were studied. The mice ChE activities on serum, brain and liver decreased by increasing of concentration and time both administration of malathion and DDVP, whereas on serum and brain the activities of the 7 days after administration decreased, and then presented the gradually slight recovery in course of time. The ChE on serum and liver showed many isozyme bands by polyacrylamide gel electrophoresis but several on brain. And isozyme bands disappeared and diffused by administration of organophosphorous insecticides and development of time. The mice liver with administration group of malathion on histopathologic test showed midzonal necrosis between central vein and portal area, and with administration group of DDVP mainly presented portal necrosis on location of potal area.