This experiment was conducted to discuss the biologically activity of yeast culture (YC) and its effects on antioxidant ability in cashmere goats. Twelve mature half-sib wethers of Inner Mongolia white cashmere goats were allotted into four groups named A1, A3, B1 and B2. Using a self-contrast designs trial, the goats in A1 and A3 groups were fed a basal diet with concentrate to roughage (C/R) ratio of 3∶7; and the animals in B1 and B2 groups were fed the basal diet with C/R ratio of 2∶8 in control period. After the control period, YC was added at level of 2.0% in A1 and B1 groups, 3.0% in A3 group and 2.5% in B2 group in YC supplement period, respectively. Blood samples used to determine the antioxidant ability were taken from the jugular vein on the last day of control period, the 15th day and the 45th day of YC supplement period. The results showed that there was no significant difference on body antioxidant ability among groups in each period (P>0.05). Compared with the control period, YC supplementation significantly decreased the activities of serum ROS in A1 (P<0.05), A3 (P<0.05) and B1 (P<0.01) group on the 15th day of YC supplement period and decreased the concentration of MDA, especially in the animals fed the diet with higher C/R ratio in A1 (P<0.01), A3 (P<0.05) group during YC supplement period. Compared with the control period, YC supplementation increased the activities of serum GSH-Px by 33.24%~142.52% (P>0.05), significant enhanced plasma SOD activities in A3 (P<0.01) and B1 (P<0.05) group. T-AOC of A1 (P<0.01), A3 (P<0.05), B1 (P<0.01) and B2 (P<0.01) groups were significantly increased at the 45th day of YC supplement period. These results indicated that YC supplementation in diets could increase the antioxidant ability of cashmere goats.［Chinese Journal of Animal Nutrition, 2010，22（3）:781-786］