This study was done to determine the toxic effect of fthalide in rats which have oral administration at levels of 100 mg/kg/day for twelve days. It was examined the hematogram and serological parameters, and also the content of cytochrome P-450, the activity of NADPH-cytochrome c reductase, glucose-6-phosphatase, cholinesterase and carboxylesterase in liver. Any significant alteration of hematogram was not found but the value of AST, LDH and content of glucose in serum were statistically increased. The content of cytochrome P-450, the activty of NADPH-cytochrome c reductase were increased but glucose-6-phosphatase were slightly decreased compare with that of control group. The activity of cholinesterase was decreased slightly and on the contrary the activity of carboxylesterase was found to be the tendeny of increase in both of liver and serum.