Acute kidney injury (AKI) is a major health concern, because AKI is related with an increase in morbidity and mortality. Anemia is related to AKI in several clinical settings. However, the relationship between anemia and AKI and the effect of anemia on long-term mortality are unresolved in critically ill patients. A total of 2,145 patients admitted to the intensive care unit were retrospectively analyzed. We calculated a threshold value of hemoglobin associated with an increased risk of AKI and used this value to define anemia. The odds ratios (ORs) and hazard ratios for AKI and all-cause mortality were calculated after adjusting for multiple covariates. The OR of AKI increased depending on the decrease in hemoglobin level and the ideal threshold point of hemoglobin linked to increasing AKI risk was 10.5 g/dL. We categorized patients into anemia (< 10.5 g/dL) and non-anemia (≥ 10.5 g/dL) groups. The risk of AKI was higher in the anemia group than the non-anemia group and this trend remained significant irrespective of the AKI development time (early vs. late) or duration (< 3 days vs. ≥ 3 days). Both anemia and AKI increased the 10-year mortality risk and this risk prediction was significantly separated by the presence of anemia and AKI. Furthermore, the risk prediction remained consistent irrespective of the AKI severity (i.e., recovery, stage, or duration of AKI). Based on these, we urge clinicians to monitor anemia and AKI in critically ill patients.