To investigate the effect of feeding rats medium-chain triglyceride(MCT), triglyceride containing primarily C8 and C10 fatty acids, it were compared to the effects of feeding triglycerides composed of long-chain triglyceride (LCT), corn oil and lard, on the serum enzyme activity. For 4 weeks rats fed a diet containing 20％ MCT or LCT · MCT, as compared with LCT, had the following effects: 1) The total lactic dehydrogenase(LDH) activities in the serum of all experimental group were significantly decreased then those of control group. 2) The activities of glutamic oxaloacetic transaminase (GOT) in the serum of all experimental group were decreased than those of control group. 3) The activities of glutamic pyruvic transaminase (GPT) in the serum of all experimental group were decreased, MCT and LCT group were singinficantly decreased than of control group. 4) The activities of α-amylase in the serum of all groups were significantly increased than those of control group. 5) According to electrophoresis, LDH of LDH isoezyme activities in MCT and Lard group were increased with those of LDH5 in corn oil group were increased than those of control gourp. It is suggested that the MCT and LCT fed to rats influence on the activity of various serum enzymes.