Abstract: Cellulase was used to improve soluble dietary fiber ( SDF) content of rice bran dietary fiber ( RBDF) .The enzymatic hydrolysis was optimized through single factor experiments and orthogonal experiments.Total, soluble and insoluble dietary fiber ( TDF, SDF, IDF) were separated respectively under the condition to evaluate their antioxidant activities.Under the condition of cellulase addition of 65 EGU per gram RBDF, enzyme pH5.0, hydrolysis temperature of 50℃, time of 3h, SDF content was the highest and up to 6.97%.Total phenolics content ( TPC) and total antioxidant capacity ( TAC) of TDF and SDF were 4.38 ± 0.30, ( 18.53 ± 1.41) mg gallic acid and 15.43 ± 0.62, ( 35.25±3.18) μmol Trolox per gram dietary fiber respectively.DPPH·, ·OH, O-2·scavenging capacity increased significantly.The three types of dietary fiber can suppress the oxidation of linoleic acid system and the antioxidant activity were higer than the antioxidant activity of 0.5mg /mL VC.TAC and reducing power were positive related to TPC ( p < 0.01) .