The aim of this study is to investigate the rumen ecology and feed digestion in Formosan Reeves' muntjac (Muntiacus reevesi micrurus). We also observed the effect of captive environment on animal digestive physiology by comparing the characteristics of gastrointestinal tract and tissue samples of ruminal papillae between captive and wild muntjac. Results revealed that the pH value of rumen fluids of captive muntjac was 6.44 and the concentration of volatile fatty acid, which was lower than that of the domestic animal. The rumen total bacteria count was 1.35 )10 8 colony counts/mL rumen fluids. The percentage of Isotrichidae in total protozoa population was lower than 20%, whereas Ophryoscolecidae was greater than 80%. The ratio of intestinal length to body length was approximately 13.9:15.1 which was similar to the concentrate selector. The morphology of ruminal papillae showed distinct difference between captive and wild muntjacs, and the length of small intestinal tract tended to be longer in captive muntjac, suggesting that morphology of ruminal papillae could be related to the dietary difference between captive and wild muntjacs.