OBJECTIVE:To study the effects of combined use of cefoperazone/sulbactam(CFS),meropenem(MRP)with le-vofloxacin (LVX) on mutant prevention concentration for Acinetobacter baumannii so as to provide a experimental foundation for preventing bacterial drug resistance. METHODS:In the test,there were groups of single use of CFS,MRP and LVX,and groups of combined use of CFS+LVX and MRP+LVX. Double dilution agar method was used to respectively detect minimal inhibitory con-centration (MIC) for standard Acinetobacter baumannii strains ATCC 19606 and 36 clinically isolated strains in all groups,and then the index of fraction inhibitory concentration(FIC)was calculated. Agar dilution method on plates was employed to detect mu-tant prevention concentration (MPC) for Acinetobacter baumannii in all groups,and then corresponding selection index (SI) was calculated. RESULTS:After combined use of CFS or MRP with LVX,synergistic effect accounted for 55%(20/36)and 50%(18/36). For standard strain ATCC 19606,after combined use of CFS+LVX and MRP+LVX,MPC reduced from 32.0 and 4.0 mg/L to 1.8 and 0.8 mg/L;For 36 clinically isolated strains,after combined use of CFS+LVX and MRP+LVX,MPC reduced from 8.0-32.0 and 1.0-2.0 mg/L to 0.25-1.0 and 0.25-0.5 mg/L. SI were all obviously reduced after combination. CONCLUSIONS:The combina-tion of CFS or MRP with LVX can reduce MPC for Acinetobacter baumannii more significantly than the single use,and narrow mu-tant selection window.