Eight hundred sixty eight Hy-Line Brown laying hens about 280 d old with similar egg production rate,were randomly divided into high temperature group (33℃),probiotics group (Bacillus subtilis+33℃) and room temperature group (26℃).The experiment was conducted for 20 d to investigate the feasibility and mechanism of B. subtilis HDRaBS1 on alleviating animal heat stress.The results showed that the egg production rate,average daily feed intake and average egg weight of the probiotics group increased by 2.60% (P<0.05),2.91% (P>0.05) and 0.96% (P>0.05),respectively,compared with the high temperature group,but were less than those of the room temperature group.In addition,the diarrhea rate and broken egg ratio of the probiotics group were reduced,serum endotoxin and IL-1were reduced by 37.41% (P>0.05) and 20.98% (P<0.05),while IL-10 expression was increased by 41.05% (P>0.05) than those of the high temperature group.Moreover,in the probiotics group,the mRNA expression of many genes in the cecum,including the tight junction occludin,ZO-1 and JAM-A,and the mucosa repair gene of EGF were significantly up-regulated (P<0.05),intestinal villus height (P<0.05) was improved,while no pronounced variation of the crypt depth was observed (P>0.05).Therefore,adding B.subtilis HDRaBS1 could effectively alleviate the symptoms of heat stress-induced laying hens.