In order to study the effects of different diets on the amino acids content in duodenum digesta of cows, 6 kinds of diet with 2 kinds of roughage (corn stover silage and corn stover) and 3 kinds of concentrate to roughage ratio （3∶7，4.5∶5.5 and 7∶3） were used as feed in the research. Three healthy Holstein cows with permanent cannulas at the proximal duodenum with the body weight of 550～600 kg were selected according to 3×3 Latin design. The experiment was divided into 2 stages with 3 periods. The results showed that the kinds of roughage had little influence on content of amino acids, while the ratio of concentrate to roughage had larger influence. The influence of dietary composition on the content of amino acids changed with the kinds of amino acids. The most affected amino acids were Met, Thr and Leu, and the Val, Lys, Phe and His were the second, while Arg and Ile changed little with the dietary composition. The results indicated that the kinds of roughage and the ratio of concentrate to roughage could influence the content of amino acids in duodenum digesta.［Chinese Journal of Animal Nutrition, 2010，22（2）:481-486］