We investigated the effects of resveratrol supplementation on in vitro ruminal fermentation and growth performance of Hanwoo calves. Treatment with three resveratrol concentrations (0%, 0.1%, 0.3%, and 0.5%) was used for in vitro ruminal fermentation. Resveratrol concentrations and pH of rumen fluid were negatively correlated (p < 0.05); therefore, total gas production, total volatile fatty acids, and acetate, propionate, and butyrate levels were significantly higher in the treatments than in the control at all time periods (p < 0.05). The appropriate resveratrol concentration that could be added without negative effects on the rumen was 0.3%. In farm experiments, we divided 14 Korean cattle calves into control (C) and 0.3% resveratrol (T) groups. There were no significant differences in the daily weight gain, feed conversion, final body weight, body length, withers height, and height at hip cross in the resveratrol-fed Hanwoo calves. Immunoglobulin G level was significantly higher in the treatment than in the control (p < 0.05), but IgA and IgM levels did not differ. Supplemental feeding of resveratrol is beneficial to in vitro ruminal fermentation, but it is important to supplement it at 0.3%. Furthermore, resveratrol affects calf immunoglobulin G.