Brewers’ spent grain (BSG) is the most common by-product of the brewing industry, contains about 16.8% cellulose, 28.4% non-cellulosic polysaccharides and 27.8% lignin, which is a good raw material for industrial production of soluble dietary fiber (SDF).The antioxidant activity of crude dietary fiber (CDF) and grade dietary fiber (GDF) isolated from BSG was investigated in vitro. The scavenging hydroxyl radical capability of CDF and GDF was respectively reached to15.4% and 69.2% at the concentration of 0.1mg /mL. DF concentration from 0.02mg /mL to 0.1m g /mL was used. The scavenging capability of CDF and GDF to superoxide anion radical was increased from 10.68% and 12.33% to 35.78% and 78.39%. Both of the two DF showed some effect in scavenging superoxide radical and 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) radical with the concentration increase. The result showed that BSG DF can be used as a good additive with some functionality.