Abstract: Objective: To explore the role of the prt P gene of Lactobacillus casei ( 21858) in it's adhesion. Methods: Using red homologous recombination method to build 21858 prt P gene deletion mutant was built.And the growth curve, hydrophobic, auto-aggregation, the rate of intestinal mucus adhesion and the adhesion of cells were measured. Results: The growth curve was similar to the mutant strains.The hydrophobic rate of mutant strains was 44.1% greater than 23.9% of the parent strains. The auto-aggregation rate of mutant strains at each time points were less than the parent plants, and intestinal mucus adhesion rate of mutant strains was less than the parent plants.The adhesion of mutant strains to both cells were less than the parent plants.Conclusion: The prt P genes associated with Lactobacillus casei 21858 adhesive, is an important factor in determining the adhesion of lactic acid bacteria.