The effect of various lipid emulsions on the development of fatty liver during total parenteral nutrition (TPN) was investigated in rats given TPN for 7 days. Medium-chain triglycerides (MCT), long-chain triglycerides (LCT), chemically defined triglycerides (CDT; structured lipid with a high purity of 94.3%), and a mixture of MCT and LCT (MIX) were prepared as the lipid emulsions. TPN provided 350 kcal/kg/day, with a nonprotein calorie/nitrogen ratio of 160. The TPN-1 group received 10% nonprotein calories and the TPN-2 group received 30% nonprotein calories. MCT TPN was found to have some disadvantages, especially with regard to nitrogen balance and plasma albumin levels. Total cholesterol and phospholipids tended to be high in the MCT TPN group. The hepatic lipid content was higher in the lipid-free TPN and the MCT TPN groups, and lower in the CDT and LCT TPN groups. Histologically, the livers of the MIX, CDT, and LCT TPN groups showed less fatty change than those of the FREE and MCT groups.