Abstract: Rumen-protected methionines(RPMet) were obtained from polyoxylate Ⅳ(M1), polyoxylate Ⅳ and ethyl-cellulose(M2), polyoxylate Ⅳ and ethylcellulose and hydroxyprpoyl methylcellulose(M3), ethyl-cellulose(M4), polyoxylate Ⅳ and hydrogenated vegetable oil(M5),and hydrogenated vegetable tallow(M6).Rumen-protected lysines(RPLys) were obtained with polyoxylate Ⅳ and ethyl-cellulose(L1), polyoxylate Ⅳ and hydroxyprpoyl methylcellulose(L2),polyoxylate Ⅳ and hydrogenated vegetable oil(L3),ethyl-cellulose and hydrogenated vegetable oil(L4). The stability of RPMet and RPLys was tested by in vitro and in situ.After incubating for 4, 8, 24 and 48 h in the rumen ,the ruminal release rate of nitrogen was lower and ranged from 11.72% -50.67% and 35.70%-72.09% in M5 and L3, respectively . However ,when incubated in the buffer solution(pH= 6.6) for 4, 8, 24 and 48 h, nitrogen release rate ranged from 24.67%-38.44% and 42.05%-75.02% in M5 and L3, respectively. There was a significant positive linear relationship (RM2=0.867 5、RL2=0.963 0) of the degradability of RPMet and RPLys between in vitro and in situ.Nitrogen release rate was 100 % in M5 and L3 in the small intestine and the buffer solution(pH=2.4).