The present study was examined the ability of medium- and long-chain triglycerides (MLCT) to activate hepatic fatty acid oxidation and lipogenic enzymes, and the ability was compared with that of medium-chain triglycerides (MCT) and long-chain triglyceride rapeseed oil (LCT). Emulsified samples of three test oils were administered orally to Wistar rats, and were measured the hepatic fatty acid oxidation enzymes (carnitine palmitoyltransferase, acyl-CoA dehydrogenases, and acyl-CoA oxidase) activity and a lipogenic enzyme (fatty acid synthase) activity in the liver after 30 min of administration spectrophotometrically. Among the acyl-CoA dehydrogenases measured, the highest activity was seen in particular in short-chain acyl-CoA dehydrogenase and medium-chain acyl-CoA dehydrogenase following MLCT administration. On the other hand, no significant differences were observed in the lipogenic enzyme activity. Although MLCT contained only one-seventh amount of medium-chain fatty acids (MCFA) in MCT composed exclusively MCFA, these results indicate that the amount of MCFA in MLCT would seem to the minimal effective dosage to activate hepatic fatty acid oxidation enzymes as seen in MCFA studies to date.