Abstract: Extracellular protease, extracellular amylase, and extracellular cellulase are the important virulence factors of Xanthomonas campestris pv. campestris（Xcc）, and their expressions are under strict control. Our laboratory previously found that, in Xcc8004, deletion of rsmA, a gene encoding the post-transcriptional regulator RsmA, resulted in marked drop in yield of extracellular amylase and extracellular cellulase, but not affect the yield of extracellular protease; and thus concluded that RsmA positively regulates the production of extracellular amylase and extracellular cellulase, but not regulates extracellular protease production. To further determine whether RsmA is involved in the control of extracellular protease expression, in this study, the rsmA-overexpression strain OErsmA was constructed, and the extracellular protease yield of OErsmA was tested and compared to that of WT/pB（the wild-type strain carrying the empty overexpression vector pBBad18K）. The results showed that the extracellular protease yield of OErsmA was significantly reduced compared to that of WT/pB, demonstrating that RsmA inhibits extracellular protease production of Xcc. Northern blotting analysis showed that the accumulation of the mRNA of the major extracellular protease gene prtA in OErsmA was similar to that in WT/pB, while EMSA（electrophoretic mobility shift assay） results showed that（His）₆-RsmA can bind specifically with the SD sequence（shine-dal-garno sequence） region of prtA mRNA, indicating that RsmA inhibits extracellular protease production through inhibiting the translation initiation, but not the transcription, of prtA mRNA.