Objective:To investigate the inhibitory effect of gallic acid on Pseudomonas aeruginosa biofilm. Methods:From January to June 2020, crystal violet staining was used to screen clinically isolated Pseudomonas aeruginosa biofilm strains in Taizhou Hospital of Integrated Traditional Chinese and Western Medicine. The minimal inhibitory concentration (MIC) of gallic acid against Pseudomonas aeruginosa was detected by the microdilution method. The adhesiveness of gallic acid to Pseudomonas aeruginosa and the minimum inhibitory membrane concentration (SMIC) were determined by (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) (XTT) assay. Results:PA08, PA12, PA18, PA35, PA53 and ATCC27853 strains were screened and used as test strains. The MIC of gallic acid against PA08, PA12, PA18, PA35, PA53 and ATCC27853 strains was 150 mg/L, 150 mg/L, 75 mg/L, 150 mg/L, 150 mg/L and 150 mg/L, respectively. Gallic acid at 75 mg/L could significantly inhibit the early adhesion of PA18 strain ( t = 3.766, P < 0.05). Gallic acid at 150 mg/L could significantly inhibit the early adhesion of PA08, PA12, PA18, PA35, PA53, ATCC27853 ( t = 4.562, 3.787, 6.769, 11.29, 5.719 and 7.251, all P < 0.05). Gallic acid at 300 mg/L could significantly inhibit the adhesion of PA18 strain at 6 hours ( t = 6.012, P < 0.05). The SMIC 50 of PA12, PA35, PA53 was 75 mg/L, and that of PA08, PA18, ATCC27853 was 150 mg/L. Conclusion:Gallic acid can effectively inhibit the early adhesion of Pseudomonas aeruginosa and affect its biofilm formation.