【Abstract】 Objective Long-term peritoneal dialysis (PD) may lead to peritoneal fibrosis and ultrafiltration failure. It has been demonstrated that the rennin-angiotensin system (RAS) plays a key role in the regulation of peritoneal function in rats on peritoneal dialysis. We investigated the effects of angiotensin-converting enzyme inhibitor (ACEI) and angiotensin receptor blocker (ARB) on long-term PD patients. Methods We analyzed data from 68 patients treated with PD in this hospital for at least 12 months, during which at least 2 peritoneal equilibration tests (PET) were performed. Thirty-nine patients were treated with ACEI or ARB (ACEI/ARB group); and 29 patients received none of the above drugs during the entire follow-up period (control group). The expression of fibronectin, transforming growth factor-β1 (TGF-β1), aquaporin-1 (AQP1) and vascular endothelial growth factor (VEGF) in the overnight effluent before PET were examined by enzyme-linked immunosorbent assay (ELISA). Results The demographic data showed no difference between the 2 groups, nor did the prevalence of peritonitis in the study period. At the beginning of study, no difference was found in residual renal function between ACEI/ARB group (4.7±1.9ml/min) and control group (4.6±2.0ml/min). After the treatment for 12 months, residual renal function decreased to 3.17±1.35mL/minute in ACEI/ARB group and to 2.78±1.41mL/minute in control group (P= 0.014), the glucose concentration ratio in dialysate at 0h and 4h (D4/D0) decreased slightly in both groups (P>0.05), the ratio of creatinine in dialysate and in plasma at 4h (D/Pcr) was higher in control group (0.15±0.03, P<0.05) than in ACEI/ARB group (0.08±0.0313), and ultrafiltration volume was lower in control group (-87.5±42.6ml/4h) than in ACEI/ARB group (-161.8±61.4ml/4h, P<0.05). Fibronectin, TGF-β1 and VEGF in overnight effluent increased in control group (P<0.05), but not in ACEI/ARB group (P>0.05). Conclusion ACEI and ARB appear to decelerate the deterioration of ultrafiltration efficiency and residual renal function, and to effectively protect against peritoneal fibrosis in long-term peritoneal dialysis.