Abstract: This experiment was conducted to study the effects of AA on rumen microbes and fermentation in vitro. Four Xuhuai wether goats fitted with permanent ruminal cannulas were used to provide rumen liquor in vitro. The special amino acids removal method was applied. Treatments of total amino acid(Group A), Met-removal(Group B), Lys-removal(Group C), Branch-chain amino acid-removal(Group D), Aromatic amino acid-removal(Group E)were designed. The results of the study showed that the pH-value ranged between 6.01 and 6.45, and the highest mean value appeared in group C(6.23). Concentration of NH3-N ranged from 7.98 to 29.05 mg·100 mL^-1, with the highest mean value occuered in group A(18.16 mg·100 mL^-1). The order of the restricted role of AA-specific default on rumen micro-organisms(bacteria and protozoa)was that: BCAA> ARAA>Methionine> Lysine. The highest of P/B ratio was group B(101.37%), and the lowest was group D(88.22%). The highest of microbial AA-N ratio, bacteria AA-N, protozoa AA-N was group E, group D and group E, respectively, and the lowest of them was group C. Microbial diversity was demonstrated in SSCP fingerprint clearly, which revealed that the structure of bacteria or protozoa community was altered by substrates. Amino acid influences both on fermentation and microbial community in vitro.