Objective    To evaluate the association between body-mass index and prognosis in peritoneal dialysis (PD) patients.    Methods    In this observational study of a single nephrology unit in Shanghai East Hospital, 81 incident continuous ambulatory peritoneal dialysis(CAPD) patients were included from Jan 2008 to Dec 2013, whom were followed-up by 36 months or until death. The patients were classified as underweight (BMI＜18.5 kg/m²); normal weight (18.5～23.9 kg/m²); overweight (24～27.9 kg/m²) and obese (BMI≥28 kg/m²). The patients and technique survival rates were estimated by Kaplan-Meier analysis. Cox proportional hazards analyses were used to elucidate relationship between BMI and all-cause mortality and technique failure in PD patients.    Results    The overall survival rate was similar between normal and overweight groups (P=0.96), but significantly lower in underweight group and obese group (P＜0.01 respectively). The overall technical survival rate of obese group was lower compare with normal group (P＜0.01). The main cause of technical failure was peritonitis (81.3%). BMI was positively correlated with albumin (r=0.24, P＜0.05), hemoglobin (r=0.56, P＜0.01), glucose(r=0.23, P＜0.05) and cholesterol (r=0.41, P＜0.01), but negatively correlated with Kt/V (r=-0.36, P＜0.01) and Ccr(r=-0.34, P＜0.01). In adjusted Cox proportional hazard mode 3, obese was independently associated with all-cause mortality (HR: 5.93, 95%CI: 1.10～31.79). Obese and peritonitis were independently associated with technical failure (HR: 10.33, 95%CI: 1.04～78.02 and HR: 2.74, 95%CI: 1.17～6.40 respectively).    Conclusions    Underweight and obese CAPD patients have poorer outcome. Obese CAPD patients also have lower technical survival rate. Obesity was an independent risk factor for all-cause mortality in CAPD patients.