Abstract: Pseudomonas aeruginosa H4-3 was an endophytic bacterium isolated from banana plant by Microbiological Research Center of Agricultural Bioresource Research Institute, Fujian Academy of Agricultural Sciences, this strain showed high antibacterial activity against the pathogen of banana Fusarium wilt, and its active substance was a kind of large molecular weight protein. In this study, the stability of H4-3 antibacterial protein was tested. The results showed that H4-3 antibacterial protein was tolerant to high temperature, strong acid and basic, and protease at high concentration. Ultraviolet radiation and repeated freezing and thawing had no significant effect on the activity of H4-3 antibacterial protein.