Objectives: The association between early hemoglobin levels after kidney transplantation (KT) and long-term outcomes is uncertain. We investigated the impact of early post-transplant hemoglobin levels on the clinical outcomes. Methods: We analyzed hemoglobin levels at 6 months after KT of 7,501 kidney transplant recipients (KTRs) from a nationwide cohort, the Korean Organ Transplant Registry. Factors associated with hemoglobin levels were analyzed using multivariate linear regression. KTRs were divided into 5 hemoglobin categories: <10, 10 to <11, 11 to <12, 12 to <13 (reference group), and ≥13g/dL. The primary outcome is a composite of all-cause mortality, cardiovascular events, and graft loss. The multivariable Cox regression model was used to investigate the effect of hemoglobin levels on the composite outcome. Results: The mean age was 49.6 ± 11.6 and male ratio was 60.4%. The prevalences of diabetes and cardiovascular diseases were higher and that of hypertension was lower in hemoglobin levels <10 g/dL. Female sex (β= –0.32), deceased donor KT (β= –0.15), and age (β= –0.12) had the highest standardized coefficients among significant factors associated with hemoglobin levels. The incidences of the composite outcome and each component were the highest in hemoglobin levels <10 g/dL (all P< 0.05). Hemoglobin levels <10 g/dL were associated with an increased risk of the composite outcome (adjusted hazard ratio [aHR] 3.36, 95% confidence interval [CI] 2.23–5.06, P< 0.001). Hemoglobin levels <10 g/dL were also an independent risk factor for each component of the primary outcome. Interestingly, hemoglobin levels ≥13 g/dL were significantly associated with better survival (aHR 0.43, 95% CI 0.21–0.87, P= 0.019). Conclusions: The post-transplant anemia below 10g/dL was an independent predictor of composite outcome including all-cause mortality, cardiovascular event, and graft loss. Hemoglobin levels >13g/dL showed a protective effect on patient survival. Appropriate monitoring and correction of hemoglobin should be a target of management in the early post-transplant.