Abstract: Thirty-six Simmental beef cattle (12-month-old) consuming a corn straw diet were randomly divided between four treatments supplemented by four levels of isobutyrate (0,0.02,0.04 and 0.06 g/kg·d) to evaluate the effects of isobutyrate on daily gain,dietary nutrient digestion and methane emissions. Organic matter digestibility of the cattle supplemented with isobutyrate at 0.04 and 0.06 g/(kg·d) were significantly (P<0.05) higher than that of the controls. Crude protein digestibility of the isobutyrate supplemented cattle was significantly higher than that of the controls but nitrogen-free extract digestibility was not affected. Neutral detergent fibre digestibility of the cattle supplemented 0.04 g/(kg·d) were significantly (P<0.05) higher than in the controls. Acid detergent fiber digestibility of the cattle supplemented 0.04 g/(kg·d) were significantly (P<0.05) higher than in the controls and other groups. Furthermore,final body weights were affected by isobutyrate supplementation with 0.04 g/(kg·d) (P<0.05),and the average daily gains of cattle supplemented 0.04 and 0.06 g/(kg·d) were increased significantly (P<0.05). Dry matter intake of cattle supplemented 0.04 g/(kg·d) were significantly (P<0.05) lower than in the controls. The feed conversion rates were improved significantly (P<0.05) by the supplementation of isobutyrate at 0.04 and 0.06 g/(kg·d). In addition,the methane emissions were significantly (P<0.05) reduced from cattle supplemented 0.04 and 0.06 g/(kg·d). The results indicated that average daily grain,nutrient digestion and methane emissions of Simmental beef cattle could be improved by supplemental isobutyrate. The optimal dose of isobutyrate supplementation was 0.04 g/(kg·d).