Abstract: Objective To study the synergistic inhibitory effect of N-acetylcysteine（NAC） in combination with piperacillin,ciprofloxacin and amikacin on Pseudomonas aeruginosa strainsMethods Minimum inhibitory concentrations（MICs） of NAC and three antibiotics were measured by broth microdilution test.Synergistic inhibitory effect of NAC in combination with piperacillin,ciprofloxacin and amikacin was determined by broth checkerboard assay.Fractional inhibitory concentration index was calculatedResults The MIC of NAC against most Pseudomonas aeruginosa strains was 10-40mg/ml.The NAC in combination with piperacillin,ciprofloxacin showed a synergistic effect against 33.3% and 50% Pseudomonas aeruginosa strains,respectively.The NAC in combination with amikacin demonstrated no synergistic effect or antagonism against Pseudomonas aeruginosa strainsConclusion NAC in combination with piperacillin and ciprofloxacin has an synergistic inhibitory effect against Pseudomonas aeruginosa strains.