The acute toxicity of fthalide in rat was studied in vivo by the observations of the changes in hematogram, serological parameters, content of cytochrome p-450, activities of NADPH-cytochrom c reductase, glucose-6-phosphatase, and the contents of cholinesterase and carboxylesterase in liver. Fthabde is a practically non-toxic substance(LD50 is 3.86g/kg), but rats were intoxicated with fthabde at a oral dose of 100 mg/kg for 12 days. WBC were significantly decreased and activities of ALT and LDH, on the cotrary, the content of glucose in serum were slightly increased. Cytochrome p-450 and lipid peroxide in liver were significantly increased in the fthalide-intoxicated rats. The longer administration of fthalide showed further increase of carboxylesterase activity in liver and serum, but decrease of activities of glucose-6-phosphatase and cholinesterase in liver and serum. These results show that fthatide can induce the hepatocellular injury and neurotoxicity.