Acute kidney injury (AKI) is a clinical syndrome characterized by a rapid loss of kidney function, and its diagnosis depends on an increased serum creatinine and/or decreased urinary output. AKI is common in hospitalized patients and even more common in critically ill patients. At present specific therapies have not been developed in regard to the prevention and treatment of AKI or the strategy to expedite its recovery. Renal replacement therapy is used to support the patients when AKI is serious. In recent years, studies on appropriate treatment modality and drug dosage for renal replacement therapy have become a hot issue for attention. Mortality of serious AKI remains high, particularly in critically ill patients. Some patients who survive may obtain complete or partial recovery from AKI, but in some patients it may directly advanced to end-stage renal disease. In addition, AKI greatly increases the risk of developing chronic kidney disease or exaggerates pre-existing chronic kidney disease. Early detection and diagnosis of AKI are valuable to improve patients' prognosis. New biomarkers that can be more sensitive to detect renal injury are being developed, as kidney damage usually occurs prior to the changes in serum creatinine and urinary output. However, further investigation is mandatory to confirm the effectiveness of these novel biomarkers.