The purpose of this experiment was to study the effects of rumen-protected leucine on the phosphorylation of two key factors (4E-BP1 and p70S6K) of mammalian target of rapamycin (mTOR) signal transduction pathway in the skeletal muscle of sheep. Twelve sheep were randomly allotted to 4 groups (with 3 replicates per group and 1 sheep per replicate), and fed basal diet supplemented with 0 (control group), 0.5, 1.0 and 1.5 g/d rumen-protected leucine, respectively. After 15 days, the sheep were slaughtered and the 4E-BP1 and p70S6K phosphorylation degrees in longissimus muscle were determined by Western blot technique. The results showed as follows: compared with the control group, gray values of 4E-BP1 and p70S6K phosphorylation in rumen protected leucine groups were increased (P<0.05), and the highest values were all found in 1.0 g/d group which were 0.40% and 0.85%, respectively. Therefore, dietary rumen-protected leucine supplementation can improve the phosphorylation of two key factors (4E-BP1 and p70S6K) in mTOR signal transduction pathway in the skeletal muscle of sheep, and the suitable level is 1.0 g/d.［Chinese Journal of Animal Nutrition，2011，23（1）：61-65］