Sheath blight disease (ShB) has a severe impact on the production of rice. ABI3/VP1-like 1 (RAVL1) negatively regulated the rice defense mechanism against ShB, however, this regulatory mechanism is not clearly understood. In this study, we identified that indeterminate domain 3 (IDD3) was positively regulated by RAVL1. Further, chromatin immunoprecipitation (ChIP) assay, yeast one-hybrid assay and transient expression assay indicated a direct binding between RAVL1 and the IDD3 promoter region. IDD3 was ubiquitously expressed in different tissues and at different stages, and its expression was significantly enhanced by Rhizoctonia solani infection. IDD3 exhibited transcription activation activity in yeast and IDD3-GFP was found to be localized in the nucleus. IDD3 mutants exhibited no significant differences in response to ShB, while IDD3 overexpressors were more susceptible to ShB compared with wild type (WT) plants. Furthermore, IDD3 repressors were less susceptible to R. solani than WT plants. Interestingly, the expression of brassinosteroid-related genes (D2, D11 and BRI1) was lower in IDD3 repressors and higher in IDD3 overexpressors compared with WT. However, the ChIP assay revealed that IDD3 did not directly bind to the D2 and D11 promoters. Overexpression of IDD3 in BRI1 mutant d61-1 inhibited the activity of IDD3, reducing its susceptibility to ShB compared with IDD3 overexpressor and WT plants, indicating that IDD3 negatively regulated the rice defense mechanism against ShB by activating the BR signaling pathway. Thus, our analyses provided information to enhance the understanding of the rice defense mechanism against ShB.