ObjectiveTo evaluate the  effect of azithromycin on class Ⅰ integronintegrase gene (intI1) mRNA expression in biofilmforming (BF) Pseudomonas aeruginosa(PA)．MethodsintI1 of 10 PA strains isolated from a hospital were detected, 1 strain with positive BF+intI1 was selected for culture, blank control group and three azithromycin trial groups (divided according to 3 concentrations:16 mg/L, 32 mg/L, and 64 mg/L) were set, experiments were repeated 5 times, expression of intI1 mRNA were detected by RTPCR． ResultsRelative expression of intI1 mRNA in azithromycin groups of 16 mg/L, 32 mg/L,  64 mg/L, and control group were （1.15±0.04）,（12.47±3.10）,（19.71±0.78）, and （1.00±0.00），respectively, there were significant difference among four groups（F=163.82，P＜0.001）；intI1 mRNA expression between 16mg/L azithromycin group and control group was not significantly different (P＞0.05), but among other groups were significantly different (P<0.05), intI1 mRNA expression in azithromycin groups increased with the enhancing concentration of azithromycin in culture solution .ConclusionExpression of intI1 gene mRNA in BF PA can be upregulated by the present of azithromycin，which may improve the probability of drugresistant genes, and promote drugresistant gene recombination.