Abstract: OBJECTIVE To explore the regulatory effect of berberine on biofilm and alginate associated gene expression of Pseudomonas aeruginosa. METHODS Crystal violet staining and scanning electron microscopy were used to observe the regulatory effects of berberine on the biofilm formation of P aeruginosa at different concentrations. RT-PCR was applied to detect the effects of berberine on algR, algD, lasR and rhlR gene expression contributor to biofilm formation and aliginate bio-synthesis in P aeruginosa at high, medium and low concentrations. RESULTS Compared with the control group, the biofilm thickness in the high,medium and low concentration treated group were significantly thinner at 24 h, 72 h and 168 h（P＜0.05）. The biofilm maturity in the high, medium and low concentration treated groups were significantly inhibited under scanning electron microscopy. The expression of algR,algD,lasR and rhlR genes were significantly decreased at high, medium and low concentrations of berberine（P＜0.05）. CONCLUSION Berberine exerted negative regulatory effect on the biofilm formation and alginate biosy-nthesis of P aeruginosa in a dose-dependent manner, which may be related to the inhibition of algR, algD, lasR and rhlR expression in P aeruginosa.