Abstract: The effect of acarbose addition on ruminant fermentation was investigated in three experiments. In the first and second experiments, the effects of acarbose addition on subacute rumen acidosis was studied. The final concentration of acarbose in the media was 0, 0.1, 0.2 or 0.4 mg/mL. In the first study, the substrate consisted of 0.8 g cracked corn and 0.2 g Chinese dry grass. As compared with the control, the acarbose addition increased the pH value and the ratio of acetate to propionate, and decreased acetate, propionate, butyrate, isobutyrate, total volatile fatty acid and lactic acid concentrations. In the second experiment, the substrates consisted of cracked sorghum, corn, barley and wheat. The acarbose supplement increased pH, NH₃-N, lactate concentration and the ratio of the acetate to propionate, and decreased acetate, propionate, butyrate and TVFA concentration. In the third experiment, the effect of acarbose addition on acute rumen acidosis was investigated, the pH, acetate, propionate, acetate, propionate, valerate, isovalerate and TVFA concentrations were reduced by acarbose addition, while the pH value was improved. There were no significant changes in the isobutyrate, butyrate, and isovalerate concentrations. In general, these results indicated that acarbose addition increased the pH value and reduced lactic acid concentration, and it has the potential to prevent rumen acidosis.