Abstract: The experiment was conducted to study the effects of dietary Se-enriched yeast on blood biochemical parameters and endocrine capacity of Chai Hens in summer. 360 thirty week-old Chai laying-hens were randomly divided into five groups, with three replication per group. The control group fed with basal diets containing 0.08 mg·kg^-1 Se, the testing group fed with basal diets adding 0.15, 0.3, 05, 1 mg·kg^-1 Se, respectively. Preliminary trial period was 7 days and experimental time was 50 days. The results showed as follows: With the increasing of diet selenium content, Feeding diet with 0.3 mg·kg^-1 selenium had increased the ratio of albumen and globulin (P>0.05) ; but the blood sugar had decreased(P>0.05); The activity of GPT and CK had decreased (P<0.05), and the activity of LDH and ALP had increased (P<0.05).Feeding diets of Se-yeast had decreased the activity of T3,T4 and CORT(P<0.05). The results suggested that adding 0.3-0.5 mg·kg^-1 of Se could lessen the animal body heat stress response, increase the body′s immune system. At the same time, its could improve the metabolism of material and then increase the production performance of Chai Hens.