WRKY is one of the largest families of transcription factors in plants. In this paper, transcriptional analysis revealed that the transcription of rice WRKY42 gene was occurred at seedling stage and anther, while the expression of WRKY42 protein was detected in the leaf blade at all growth stages. In the process of Xa21- mediated resistance to bacterial blight, the induction of WRKY42 protein was apparent in the late stage after inoculation; further comparison among incompatible (R), compatible (S) and mock control (M) reactions revealed similar expression pattern between R and S interactions, and the abundance of WRKY42 in both R and S interactions was significantly greater than that in mock control reaction. This evidence suggested that WRKY42 protein may play a role in the interactions between rice and Xoo. Next, the WRKY42 protein was expressed in E. coli. The purified WRKY42 protein was used to investigate its binding capacity with cis-elements in the promoter region of downstream genes using microscale thermophoresis (MST) technique. It was found that the WRKY42 protein binds to W-box-containing oligonucleotide derived from the promoter region of PR1a and PR1b specifically, and their dissociation constant (K_d) were 73.3 μmol/L and 58.3 μmol/L, respectively. Taken together, the data provide direct evidences for the function of WRKY42 to regulate downstream pathogenesis-related genes, and further support that WRKY42 play a role in the process of rice resistance to Xoo. In the last, a working model of WRKY transcription factors in rice-Xoo interactions was proposed.