This thesis included four parts. Firstly, biological and probiotic properties of the selected Bacillus licheniformis were evaluated in vitro. And then, production experiment was carried out to assay the effect of different doses of Bacillus licheniformis on the egg production, egg quality, and serum indices of heat-stressed laying hens. So, the optimal dosage was determined. At last, the influence of the Bacillus licheniformis on intestinal barrier function and microflora of heat-stressed hens was evaluated...