Abstract: Objective To study the multi-drug resistance and its regulation mechanism of Shigellae spp.Methods Fifty-six clinical isolates of Shigella were collected.Susceptibility tests of tetr acycline(T E),chloramphenicol(C),ampicillin(AM),ciproflox acin(CIP),and norflox acin(NOR)were performed in all isolates.AcrR and mar OR genes were amplified by polymerase chainreaction(PCR)respectively.The PCR products were digested by restriction endonuclease TaqI,and then an alyzed by single strand conformation polymorphism(SSCP).Results Thirty-five multi-drug strains and eleven wild type strains were selected.The rate of multi-drug resistance was 62.5%.A crR and mar OR genes were found in all strains and the lack of the two genes were not found.SSCP analysis found three multi-drug resistant strains(6 52%)carrying mutations in acrR gene and five multi-drug resistant strains(10.87%)carrying mutations in mar OR gene.No mutation was found in three wild type strains.Conclusion The Shigella spp.had high multi-drug resistance rate.The acrR and mar OR gene mutations may play an important role in the regulation of multi-drug resistance in Shigella spp.