Aim To investigate the association of metabolic syndrome(MS) with aortic stiffness according to different definitions in continuous ambulatory peritoneal dialysis(CAPD) patients,in order to find a suitable criterion for CAPD population.At the same time,to analyze the risk factors affecting aortic stiffness. Methods 155 CAPD patients were studied.Arterial stiffness was assessed by measuring carotid-femoral pulse wave velocity(PWV).Metabolic syndrome was defined by Adult Treatment Panel(ATP) Ⅲ2001,World Health Organization(WHO)1999,and International Diabetes Federation(IDF) 2007 criteria. The PWV values were compared between MS group and non-MS group,and the risk factors associated with PWV were analyzed. Results By all definitions,which include WHO 1999,IDF2007 and ATPⅢ 2001 definition,CAPD patients with MS had higher PWV compared to CAPD without MS(P<0.05).An independent association emerged between PWV and age,waist circumference,systolic blood pressure,serum glucose positively(P<0.05 or P<0.01).And PWV was associated with serum high density lipoprotein cholesterol negatively and independently in CAPD patients(P<0.05). Conclusions Arterial stiffness is increased in CAPD patients with metabolic syndrome irrespective of the definition criteria,which includes WHO 1999,IDF 2007,ATPⅢ 2001 criterion.Age and metabolic components affect arterial stiffness independently.Based on all considerations,the ATP criterion of MS was proposed for CAPD patients.