Objective To explore the effect of combination therapy of aminoglycosides with other antibiotics on reducing the mutant selective window of Acinetobacter baumannii. Methods Three aminoglycoside antibiotics (amikacin, tobramycin, netilmicin)and four frequently used antibiotics against Acinetobacter baumannii in clinical practice (cefoperazone-sulbactam, imipenem-cilastatin,ciprofloxacin and levofloxacin)were studied.The minimum inhibitory concentrations of these antibiotics against Acinetobacter baumannii ATCC1 9606 were determined by E-test.The mutant prevention concentrations of the four antibiotics against Acinetobacter baumannii alone or in combination with aminoglycosides were determined by agar dilution method.The selective index was calculated. The effect of aminoglycosides on mutant selective window of Acinetobacter baumannii was evaluated according to the change of selective index after combination. Results The selective index of cefoperazone-sulbactam,imipenem-cilastatin,ciprofloxacin and levofloxacin against A.baumannii ATCC19606 was 16,>32, 16 and 32.When combined with amikacin,the selective index was 1,2,4 and 4,respectively.When combined with tobramycin,the index was 2,2,8 and 8,respectively.When combined with netilmicin,the index was 2,4,8 and 16, respectively. Conclusions The mutant prevention concentration of the four antibiotics against Acinetobacter baumannii is significantly reduced when combined with any of the three aminoglycosides,which is helpful to decrease the incidence of mutants and control resistant Acinetobacter baumannii. Amikacin-based combination shows the most evident effect on reducing the mutant selective window of Acinetobacterbaumannii.