In order to investigate the toxicities of S-bioallethrin (5-biol) and its combination treatment with N-octyl bicycloheptene dicarboximide (MGK-264), the acute and subacute toxicity, and enzyme activity test were performed. $LD_{50}$ levels of S-biol and MGK-264 in rats are 640 mg/kg and 3, 280 mg/kg respectively. However, when rats were treated with the mixture of S-biol and MGK-264 (1 : 5 ratio), the $LD_{50}$ was decreased to 545 mg/kg. In serological analysis, ALT and LDH were increased in animals treated with the mixture. Also glucose level was significantly increased after 5 weeks in animals treated with both S-biol and the mixture. Other biochemical parameters such as cytochrome P-450 and NADPH-cytochrome c reductase in the liver and kidney were shown to be not significantly changed. Levels of total ATPase and $mg^{2+}$ ATPase were significantly decreased in the liver of animals treated with the mixture after 4-5 weeks. In addition, S-biol can alone decrease total ATPase activity. Total ATPase activity was also significantly decreased in the kidney after 5 week treatment with the mixture. Similarily, glucose-6-phosphatase activity was significantly decreased in animals treated with the mixture. When either S-biol or MGK-264 was administered, cholinesterase and carboxyesterase activities were slightly decreased but they were significantly decreased when the mixture was administered.