The microbiology and outcomes of peritoneal dialysis (PD) related peritonitis in elderly patients have not been thoroughly investigated. We aimed to investigate the microbiological distribution and clinical outcome in elderly patients with PD-associated peritonitis to guide clinical practice. We conducted a prospective, one center cohort study in Hunan province, China from September 1, 2014 to December 31, 2020. Among incident patients (n =279), basic clinical characteristics, pathogen distribution and prognosis of elderly PD patients (up to 65 years, n = 64) were compared with those of PD patients aged under 65 years (n = 215). The survival rate and technical survival rate were analyzed by Kaplan-Meier method. Among the 279 patients there were 394 peritonitis episodes, including 88 in elderly group, and 306 in younger groups. G+ bacteria were the main pathogenic bacteria in both groups (43.2% and 38.0%, respectively). Staphylococcus was the most common G+ bacteria. Peritonitis caused by fungal infection was significantly higher in elderly patients (P = 0.01), however, there is no significant difference in the proportions of G + bacteria and G- bacteria between the two groups. The most common G- bacteria was Escherichia coli. Interestingly, we found that Acinetobacter baumannii, polymicrobial infection and culture negative peritonitis in the elderly patients was significantly higher than that in other patients. Additionally, elderly PD patients had higher peritonitis-related mortality (HR=7.27, P = 0.01). However, the technical survival rate was similar (P = 0.67) in both elderly and other patients. Taken together, this retrospective cohort study found that elderly patients had a higher probability of peritonitis caused by of Acinetobacter baumannii, fungi and polymicrobial infections. In addition, the elderly peritonitis patients had a higher risk of mortality. Understanding the characteristics of microbiology and clinical outcome in elderly patients will help us to take effective measures to reduce the incidence of elderly PD-associated peritonitis.