Abstract: Bacillus cereus AR156, a biocontrol agent against a variety of soil-borne pathogens, could effectively control rice sheath blight in field. Here, the biocontrol efficacy and growth-promoting role of strain AR156 on rice was tested under greenhouse conditions, and the primary mechanism of strain AR156 in controlling rice sheath blight was also studied on both cellular and gene levels. The results revealed that AR156 could control Rhizoctonia solani with an efficiancy of 73.06%, and there was a 14.45% biomass increase in AR156-treated rice plants compared with those non-treated ones. Strain AR156 increased the activities of defensive enzymes SOD, PAL, POD and CAT, and the expression of defense related genes OsPR1b、OsPR10、OsNPR1 and ZB8. In rice plants pretreated with strain AR156 before inoculated with R. solani HNW-21, SOD or PAL activity peak reached in advance by four and two days, respectively, and the accumulation of defense related genes transcripts was rapid and extended. As a result, the resistance of those plants to rice sheath blight was strengthened.