Abstract: OBJECTIVE To study the drug resistance rate and molecular epidemiological characteristics, establish the multilocus sequence analysis (MLSA), method, define the evolutionary characteristics so as to provide guidance for clinical use of antibiotics and prevention of infection caused by this species of pathogen. METHODS The in vitro drug susceptibility testing and MLSA were conducted for 40 strains of Serratia marcescens that were isolated from Sep 2013 to Dec 2014, and the biological information was analyzed by using Splits tree and CLUSTALW software so as to reveal the prevalence trend. RESULTS The result of the in vitro drug susceptibility testing indicated that the drug resistance rate of the 40 strains of S. marcescens to 13 antibiotics varied from 10.0% to 52.5%, and the drug resistance rate to imipenem was 32.5%.Four housekeeping genes were developed based on the MLSA, the content of GC was about 60.0%.The number of alleles ranged from 14 to 16. gyrB possessed the most polymorphism sites (74).Splits tree research indicated that the majority of S. marcescens isolates were classified into one clonal complex. CLUSTALW research indicated that all the isolates clustered into 19 STs, of which 12 isolates were in ST8, and ST8 was a major outbreak genotype which was resistant to carbapenems.ST8, ST9, ST10 and ST 11 were classified into one clonal complex CC8. CONCLUSION The drug resistance rate of the S. marcescens to carbapenems is relatively high, and most of the strains are pandrug-resistant.The molecular epidemiological trends of S. marcescens are relatively slow, and its genome is highly conserved.At present, it is necessary to focus on the monitoring of prevalence of the clonal complex ST8-CC8 in S. marcescens so as to prevent its major outbreak and prevalence in hospitals.