Several epidemiological studies have indicated that metabolic syndrome (MetS) after renal transplantation is caused by an accumulation of non-immunological risks of renal transplantation, and affects the prognosis of the kidney and the patient by increasing the risk of arteriosclerosis and cardiovascular complications. The incidence of MetS in Japanese renal transplant recipients is 14.9 to 23.8%, but its effects on cardiovascular events and kidney prognosis are not clear. Here, we report the results of a longitudinal study on MetS in renal transplant recipients. A retrospective cohort study was conducted in 104 stable renal transplant recipients who attended our outpatient department from January 2006 to June 2007 and were diagnosed with MetS at least 6 months after renal transplantation until 31 December 2020, or did not have MetS. The impact of MetS on composite vascular events was examined using multivariate Cox proportional hazards analysis. The hazard ratios for the impact of MetS on composite vascular events diagnosed by NCEP Japan, NCEP Original, NCEP Asia, and IDF criteria on composite vascular events were 2.78 (95% CI: 1.15 to 6.75, = 0.024), 2.65 (95% CI: 1.04 to 6.80, = 0.042), 2.37 (95% CI: 0.93 to 6.01, = 0.070), and 1.91 (95% CI: 0.77 to 4.75, = 0.164), respectively. P for interaction was used to test the influence of each indicator, but was not statistically significant. MetS is a robust risk factor for graft loss and development of cardiovascular events in Japanese renal transplant recipients, even during long-term follow-up. This finding emphasizes the importance of monitoring and managing MetS in this population to improve long-term outcomes.