ObjectiveTo understand biofilmforming ability of Acinetobacter baumannii(A. baumannii) in clinical isolates, and evaluate the effect of biofilm formation on antimicrobial resistance. MethodsA total of 47 A. baumannii clinical isolates were collected, biofilmforming ability was detected by crystal violet staining assay, the minimal inhibitory concentration(MIC) of 12 kinds of antimicrobial agents to  biofilmforming isolates were detected when the isolates were in planktonic or biofilm formatted condition; biofilmforming ability of positive isolates at different culture condition (shaking or stable) and on different materials(glass tube or polypropylene plastic centrifugal tube) were detected. ResultsThirteen isolates (27.66%) exhibited biofilm formation. In planktonic condition, antimicrobial resistance rates of these isolates were all <35%, no isolates shown resistance to polymyxin and tigecycline, in biofilm formatted condition, resistance rates to tigecycline was 15.38%，resistance rates to the other antimicrobial agents were all 100%. Of 13 tested isolates, ≥10 isolates shown higher absorbance in the shaking condition than in the stable condition, ≥10 tested isolates shown higher absorbance in polypropylene plastic centrifugal tube than in the glass tube. ConclusionThe resistance of A. baumannii to antimicrobial agents is greatly changed after the formation of biofilm, which may results in the failure of antimicrobial therapy for infection.