Abstract: [Objective] In order to rationally determine the optimal supplementation level of Selenium-enriched Yeast in diet of Ujumqin Sheep in Xilingol region of Inner Mongolia and to provide theoretical basis for the promotion and application of Selenium-enriched Yeast in local mutton sheep industry, the effect of dietary supplementation of Selenium-enriched yeast on immunoglobulin and key cytokine of Ujumqin Sheep was evaluated in this study. [Methods] The experiment was conducted by randomized design with a single factor. A total of 240 healthy wether of Ujumqin Sheep were included in this study and were randomly divided into 4 groups（ Ⅰ, Ⅱ, Ⅲ, Ⅳ group）. The group Ⅰ was served as control group, of which the diet was supplemented with 0.3 mg/kg of inorganic selenium（sodium selenite,DM basis）. The Ⅱ, Ⅲ and Ⅳ groups were served as experimental groups, of which the diet were supplemented with 0.3, 0.6, 0.9 mg/kg of Selenium-enriched Yeast（DM basis）. The pre-feeding period lasted for 15 d and the formal-feeding period lasted for 60 d. [Results] The serum content of IgM, IgG, IgA and IL-1, IL-2, IL-6 of Ujumqin Sheep were significantly increased when their diet was supplemented with Selenium-enriched yeast. [Conclusion] The dietary supplementation of Selenium-enriched yeast was able to enhance the immunity function of Ujumqin Sheep. In view of the feeding cost and immunopotentiation effect, supplementation level of 0.6 mg/kg Selenium-enriched yeast（DM basis） in diet was optimal and recommended.