Objective: Peritoneal dialysis(PD)-associated peritonitis is a common and major complication of PD and the most common cause of technical failure of PD. The presence of bacterial biofilm may be an important factor leading to refractory or recurrence of peritonitis. To investigate the formation and characteristics of bacterial biofilms on PD catheters after peritonitis-associated catheter removal. Methods: The patients with maintenance PD who were regularly followed up in the Peking University People' s Hospital from June 2007 to January 2022 were retrospectively analyzed. The patients who withdrew from PD because of peritonitis and removed the PD catheter in our hospital and underwent the scanning electron microscope examination of the catheter were selected. The general information of the patients, the electron microscope results of the PD catheter and the bacterial culture results of the PD fluid were summarized. Results: (1) A total of 18 patients were included, 11 were female (accounting for 61.1%). The average age of the patients was (59.1±11.5) years, and the average duration of dialysis was (80.1±47.4) months. Primary kidney diseases were predominantly chronic glomerulonephritis (55.6%), followed by diabetic nephropathy (27.8%), and others (16.6%). The reasons for catheters removal in 18 patients were refractory peritonitis in 11 cases, recurrent peritonitis in 5 cases, and fungal peritonitis in 2 cases. (2) 16 of the 18 patients (88.9%) had catheter bacterial biofilm, and the bacterial biofilm forms were all cocci. Some were arranged in grape-like shapes, and their diameters ranged from about 500 nm to 1 000 nm. The bacterial culture results of peritoneal dialysis fluid showed that the three most common pathogens were Escherichia coli, methicillin-sensitive Staphylococcus aureus (MSSA), and Staphylococcus epidermidis. (3) Among the 18 patients enrolled, 13 patients (72.2%) had peritonitis in the past. The causative bacteria of peritonitis in 9 patients were cocci, including coagulase-negative Staphylococci (Staphylococcus suis, Staphylococcus surface, Staphylococcus xylosus, Staphylococcus warneri), Staphylococcus aureus, Streptococcus (Streptococcus salivarius and Aerococus viridans). Conclusion: Bacterial biofilm formation on the inner surface of PD catheter is common in peritonitis-associated catheter removal patients. Not all PD catheters removed due to peritonitis have bacterial biofilms. Bacterial biofilms and peritonitis pathogens may not be consistent.