The experiment was conducted to study the effects of different levels of rumen-protected leucine supplementation on protein synthesis in sheep using the one-time large doses of perfusion method. Twelve sheep were allotted to 4 groups, and fed basal diets added with 0 (control), 0.5, 1.0 and 1.5 g/d of the rumen-protected leucine for 15 days, respectively. After 15 days, all sheep were administered a flooding dose of L-［D5］-phenylalanine in jugular vein and the blood and skin tissue samples were collected. Then the sheep were killed at 90 min to measure the fractional protein synthesis rates (FSR) and the synthesis content of protein in biceps femoris, longissimus dorsi muscle and liver after pre-treatment by GC-MS. The results showed that the sheep fed diets with the rumen-protected leucine supplementation had greater FSR in longissimus dorsi muscle and biceps femoris (P<0.05), but had no significant effects in liver (P>0.05). The rumen-protected leucine significantly increased the protein synthesis in biceps femoris, longissimus dorsi muscle and liver (P<0.05). The results suggested that 1.0 g/d of the rumen-protected leucine supplementation in diet could get the best effects.［Chinese Journal of Animal Nutrition, 2010，22（4）:951-955］