Abstract: phcA is an important transcriptional factor in the regulatory network of Ralstonia solanacearum phenotype conversion. In order to illuminate its function in the regulator network, based on the sequenced genome of FQY_4, a maker-free FQY_4 phcA^- mutant was constructed by the method of the allelic exchange, and the expression of several related pathogenic genes that regulated by the phcA were analyzed. The results showed that, compared with wild FQY_4, the expressions of pathogenic genes regulated by phcA, including PME, tek, epsE, EGL, xpsR and hrpB, were significantly inhibited in FQY_4 phcA^- mutant, and their value of Log₂(RQ) were down-regulated by 6.97, 10.14, 8.79, 6.35, 9.61 and 9.56 fold, respectively. It is concluded that phcA is a key regulator in pathogenic regulatory networks of FQY_4.