ObjectiveTo understand clinical distribution and antimicrobial resistance of clinically isolated Serratia marcescens(S. marcescens), and provide basis for rational use of antimicrobial agents, as well as prevention and control of infection. Methods427 S. marcescens strains isolated between January 1, 2012 and December 31, 2015 were analyzed, antimicrobial susceptibility testing were performed by disk diffusion method. Results427 S. marcescens strains  were mainly from respiratory tract (70.26%), among which the majority were from sputum(64.87%). S.marcescens  were primarily from intensive care unit(ICU, 19.44%), department of integrated traditional Chinese and Western medicine(15.46%) as well as rehabilitation department (13.58%). The resistance rates of S. marcescens to cefoperazone/sulbactam, ertapenem, cefepime, ceftazidime, amikacin, imipenem, levofloxacin, and piperacillin/tazobactam were all＜10%; resistance rates to ciprofloxacin, gentamicin, tobramycin, ceftriaxone, sulfamethoxazole/ trimethoprim (SMZ/TMP), and aztreonam were 10%-30%. Difference in the resistance rates of S. marcescens to cefoperazone/sulbactam, ciprofloxacin, ceftriaxone, amikacin, aztreonam, and SMZ/TMP during 4 years were statistically significant (P＜0.05). In 2012-2013, resistance rates of S. marcescens to cefoperazone/sulbactam, ciprofloxacin, ceftriaxone, aztreonam, and SMZ/TMP increased obviously, then resistance rates tend to be stable,  while resistance rates to cefoperazone/sulbactam decreased. ConclusionSusceptibility of S. marcescens
 to most antimicrobial agents are high, but resistance had increasing tendency;susceptible rates of S. marcescens to ertapenem, ceftazidime, levofloxacin, and piperacillin/tazobactam are all high, and can be used as the empirical medication for the treatment of related infection.