The objectives of this study were to examine the effect of dipeptidase inhibitor (DI) on the concentration of NH₃-N, VFA and peptide N in rumen. Four Small-Tailed Han rams fitted with rumen fistula were fed with pelleted diets containing DI of different concentrations at four ten-days’ experimental periods, respectively. Rumen fluids were taken through the fistula at last two days of each period. The results indicated that DI inhibited the release of NH₃-N severely (P<0.05). In addition, the peptide N concentration increased (P<0.05) with the increase of DI concentration. However, the VFA concentrations, except propionic acid, were not affected.