To investigate the relationship between red blood cell distribution width (RDW) and residual renal function (RRF) in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Seventy‐seven CAPD patients were enrolled in this study. According to receiver operator characteristic (ROC) curve analysis, patients were divided into high RDW (RDW > 14.95%) and low RDW (RDW ≤ 14.95%) groups. The data of baseline clinical, biochemical parameters, comorbidities, medication status, peritoneal function, and dialysis adequacy were compared. Survival curves were calculated using Kaplan–Meier method. Cox regression model was employed to analyze risk factors of decline in RRF. The overall median survival time was 24 months, the median survival time of high RDW group (46 patients) and low RDW group (31 patients) were 24 and 12 months, respectively. Compared with the low RDW group, patients in the high RDW group were older, higher rate of decline RRF and white blood cells count as well as lower total Kt/V (all p < 0.05). Kaplan–Meier survival curves showed that the low RDW group had higher survival of RRF compared with the high RDW group (p < 0.001). Multivariate Cox regression analysis showed that high RDW was independent risk factor for decline of RRF(hazard ratio = 1.441, 95% confidence interval: 1.089–1.905, p = 0.01). Increased baseline RDW is associated with decline of RRF in CAPD patients and RDW can be stratified as a valuable indicator for the risk of RRF decline.