Background: Anemia is associated with significant adverse outcomes in kidney transplant recipients (KTRs). However, the association between early hemoglobin levels after KT and long-term clinical outcomes is uncertain. We investigated the clinical impact of hemoglobin levels at 6 months after KT on posttransplant outcomes. Methods: We analyzed 7,501 KTRs from a nationwide cohort data, the Korean Organ Transplant Registry (KOTRY). KTRs were divided into six hemoglobin categories: <10, 10 to <11, 11 to <12, 12 to <13, 13 to <14, ≥14 g/dL. The multivariable Cox regression model was used to investigate the effect of hemoglobin levels on all-cause mortality, cardiovascular events, and graft loss. Results: The mean age was 49.6±11.6 and male ratio was 60.4%. The prevalence of diabetes and cardiovascular diseases were higher and that of hypertension was lower in hemoglobin levels 10 g/dL. There were 122 patient (1.4%) deaths, 568 (6.7%) cardiovascular events, and 200 (2.4%) graft losses during the study period; the incidences of each outcome were the highest in hemoglobin levels <10 g/dL (all P<0.05). Hemoglobin levels <10 g/dL was associated with increased risk of all-cause mortality, cardiovascular events, and graft loss compared with hemoglobin of 12 to <13 g/dL as reference (adjusted hazard ratio [aHR] 4.82, 95% confidence interval [CI] 2.69–8.65, P<0.001; aHR 1.76, 95% CI 1.06–2.94, P=0.030; aHR 9.79, 95% CI 5.54–17.3, P<0.001, respectively). Hemoglobin levels ≥14 g/dL were independent factors for better mortality (aHR 0.32, 95% CI 0.14–0.73, P=0.007). Conclusions: The posttransplantation anemia below 10 g/dL was an independent predictor of all-cause mortality, cardiovascular event, and graft loss in KTRs. However, hemoglobin levels greater than 14 g/dL showed a protective effect on patient survival. Appropriate monitoring and correction of hemoglobin should be a target of management in the early period after KT.