Abstract: 【Objective】 The aim of this study was to investigate the effects of tannin additives on performance and blood biochemical parameters in fattening sheep. 【Method】 In the experiment， 30 fattening sheep aged five months and weighing 25~30 kg were randomly divided into three groups with ten replicates in each group. They were blank control group: group A， fed basal diet； experimental group: group B supplemented with 10 g/d tannin in basal diet and group C supplemented with 15 g/d tannin in basal diet. The prefeeding period of the trial was 7 days， the positive feeding period was 42 days， and the entire trial period was 49 days. At the end of feeding， their growth performance， closely related serum biochemical parameters and apparent digestibility of nutrients were measured. 【Result】 The daily gain of group B and C was higher than that of group A； compared with group A， the alanine aminotransferase level of group B and C was significantly increased （P<0.05）； the serum biochemical indicators such as total protein， albumin， globulin， creatinine and glucose of group B and C were not significantly affected； compared with group A， the alkaline phosphatase content of group B was significantly increased （P<0.05）， with no significant difference in group C； the apparent digestibility of crude protein of group B was lower than that of groups A and C（P>0.05）， and there were no significant differences in the apparent digestibility of dry matter， crude fat， calcium and NDF. 【Conclusion】 The addition of 10 and 15 g/d tannin additives to the grain of fattening sheep days could improve the performance of fattening sheep and had a greater effect on the contents of alanine aminotransferase， alkaline phosphatase， urea and crude protein.