The purpose of this study is to examine the effects of highly purified structured lipids on serum and liver lipid profiles in rats. We also investigated in vitro hydrolysis of lipid emulsions by porcine pancreas. Hydrolysis rates of medium chain (M)-linoleic (L)-medium chain (M) types were 2 to 3 times higher than those of L-M-L types. The diet containing structured lipids or corn oil was administered to rats for 4 weeks. There were no significant differences in growth and food efficiency. Serum cholesterol levels were significantly lower (P<0.05) in the 2-octanoyl-1,3-dilinoleoyl-glycerol, 2-linoleoyl-1,3-didecanoyl-glycerol, and 2-decanoyl-1,3-dilinoleoyl-glycerol groups than in the corn-oil group. Serum triglyceride levels were significantly lower (P<0.05) in rats fed L-M-L types than those in the other groups. Serum non-esterified fatty acid (NEFA) and beta-hydroxybutylate levels were significantly higher (P<0.01) in rats fed M-L-M types than those of the other groups. These results indicate that the feeding of highly purified L-M-L types could effectively improve serum and liver lipid profiles and that M-L-M types may be a preferable substrate for the pancreas and contribute to energy supply in rats.