The object of this study is to investigate the toxicity of S-biol (d-allethron-d-transchrysanthemate) and the mode of action between other synthetic pyrethroid insecticides and S-biol in rats. Rats were treated daily with S-biol (25 mg/kg, 50 mg/kg, 100mg/kg) by oral administration for 5 weeks. The experimental results were summerized as follows: Biochemical parameters such as LDH and Glucose in serum were much more increased in control groups. No significant hematological change excepts for MCHC in rats treated with S-biol 100 mg/kg were observed in all groups compared to control groups. In animals treated with S-biol for 4∼5 weeks, the levels of cytochrome P-450 in the liver were significantly increased. In renal microsomal fractions, however, no significant changes of cytochrome P-450 contents were observed. The activitis of ATPase in groups treated with S-biol (50 mg/kg, 100 mg/kg) were decreased compared to those in other groups. TBA values and activities of glucose-6-phosphatase in the liver were increased a little in the groups treated with S-biol (100 mg/kg) for 5 weeks. The activities of cholinesterase in hepatic and serum were not significantly changed in all groups but slightly decreased in animals treated with high dose of S-biol (100 mg/kg). The activities of carboxylesterase in serum and in the liver were slightly increased but not significantly changed.