Objective To investigate the protective role of the surface protein LiaX in Lacticaseibacillus paracasei L9 against external stresses, such as bile salts, antibiotics, and the gastrointestinal environment.Methods A LiaX-overexpressing strain was constructed and the protein was purified. Spent media assays, in vitro simulated digestion, and exogenous protein supplementation experiments were comprehensively employed to evaluate the effect of LiaX on the survival rate of the strain under digestive, bile salt, and antibiotic stresses.Results The LiaX-overexpressing strain LPL9psip0968his was successfully constructed, and the LiaX protein was isolated and purified. Spent media assays and exogenous addition of purified LiaX protein showed that the lysate of the LiaX-overexpressing strain exerted a significant protective effect on the bacteria under various stress conditions. In vitro simulated digestion experiments showed that LiaX significantly improved the survival rate of the strain during simulated gastric and intestinal digestion.Conclusion LiaX protein significantly enhances the stress resistance of the strain.