Abstract: In vitro and in Sacco techniques were used to identify the stability of the rumen-protected Leucine （RPLeu） in the artificial saliva and rumen of the Inner Mongolia White Cashmere Goats （IMWCG）, and its digestibility in the duodenum. The coated amino acids were incubated for 2,4,8,12,16 and 24 h in the artificial saliva, rumen and duodenum. Results showed that： Release rate of the RPLeu was improved with the cluture time;Release rate of the RPLeu in saliva ,rumen and duodenum were10.63 % ,25.82 % and 85.27 % after 8 hour.It showed that the tureen-protected Leucine had a good stability in saliva and rumen ,and it had a good digestibility in the duodenum.