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Objectives: To investigate the mechanisms and prevalence of carbapenems resistance in clinical isolates of Serratia marcescens recovered from six hospitals in Zhejiang, China.Methods: A total of 147 S.marcescens isolates were collected from six hospitals in Zhejiang of China.Antibiotic susceptibilities test was performed according to CLSI 2011 guidelines.Carbapenemases were detected by modified Hodge test (MHT) and Klebsiella pneumoniae carbapenemase (KPC) producing strains were identified by chromogenic agar medium.Resistance genes associated with carbapenemases, class C chromosomal cephalosporinase (AmpC) and efflux pumps were analyzed by PCR and sequencing.The transferability of carbapenemase genes was testified by conjugation experiment and the contribution of efflux pumps to resistance was investigated with Carbonyl cyanide m-chlorophenylhydrazone(CCCP).Investigations also included molecular typing of strains by PFGE and outer membrane proteins (OMPs) profiling by SDS-PAGE.Results: According to the results of antibiotic susceptibilities test, we found that 11 out of 147 (7.5%) S.marcescens isolates showed resistance to carbapenems, and none of them was susceptible to ertapenem.Furthermore, 90.9% (10/11)isolates showed resistance to all three carbapenems (imipenem, meropenem and ertapenem).Of the 11 carbapenemresistant isolates, 90.9% (10/11) isolates were identified by MHT to be capable of carbapenemase production, and the result of chromogenic agar medium showed they were KPC-possessing isolates.However, carbapenemase genes were detected in these 11 clinical isolates, which involved the blaKPC from ten isolates and the blaIMP from one isolates.Among the 11 clinical isolates, 10 carried blaEBC, 9 carried blaMOX.Among the 11 carbapenemase-possessing clinical isolates, blaKPC of 7 isolates were successfully transferred to E.coli C600.The presence of CCCP showed significant effect on carbapenem MICs, but PCR analysis for efflux pumps genes including acrA, acrB, MexB, MexR showed negative results.SDS-PAGE revealed that there was no OMPs deficiency among all these isolates.PFGE profiling revealed that there were three subgroups among 11 S.marcescens isolates.Conclusion: The production of KPC-2-type carbapenemase is the main contributor to carbapenems resistance for all these 11 S.marcescens in our study.