In the present study, the oxidation of palmitic acid to carbon dioxide and the difference of incorporation rate of the same and oleic acid into embryo lipids were examined. To test the exact role of fatty acids for energy production, the oxidative rates of exogenous palmitic were assessed in M16 medium with and without carbohydrate substrates. The oxidation of palmitic acid in the medium with carbohydrates was lower than that without carbohydrates in the blastocyst stage. Incorporation rates of both palmitic and oleic acids into embryo lipids increased significantly from the 2-cell to the blastocyst stage (P<0.05), whereas the incorporation rates of palmitic acid were significantly higher than those of oleic acid at most of the cell stages except for the blastocyst stage (P<0.05). In the neutral lipid fraction, ³H-palmitic acid was predominately distributed in triacylglycerol species and a little in the other glycerides (P<0.05). However, higher percentages of ¹⁴C-oleic acid were recovered in fatty alcohols, diacylglycerols and monoacylglycerols. In the polar lipid fraction, the percentages of ³H-palmitic acid in choline and ethanolamine phosphatides were significantly higher than those of oleic acid among all cell stages except the 2-cell stage (P<0.05), whereas the percentages of ¹⁴C-oleic acid in inositol and serine phosphatides were significantly higher than those of ³H-palmitic acid during preimplantation development (P<0.05). According to the comparison of incorporations into the embryo lipids and distributions in individual lipid classes between palmitic and oleic acids, it could be inferred that exogenous oleic acid is not a main energy substrate but a major intermediate for synthesis of various embryo lipids.