Background　Acute kidney injury(AKI) is common after major surgery and in critically ill patients, and is associated with increased mortality, greater cost, and prolonged Intensive Care Unit and hospital stay. Despite attempts to develop therapies for preventing or attenuating AKI have been going, but only limited success has achieved. One major reason for this lack of success may be the result of delayed implementation due to the inability to detect AKI early.　Objective　This review aimed to describe the new early biomarker of AKI-neutrophil gelatinase-associated lipocalin(NGAL).　Content　The main contents of this article include the common cause of unsuccessful treatment for AKI, limitations of traditional biomarkers to identify AKI, requirements of optimal biomarkers for AKI, the nature and source, role and pathophysiological triggers of NGAL, clinical evidence of NGAL as a biomarker for AKI, clinical value and limitations of NGAL, etc.　Trend　Early identification of AKI with rapid and reproducible biomarkers is a critical step toward improving patient's outcomes. NGAL appears to fulfill many characteristics of an appropriate "real?蛳time" biomarker for AKI detection. Furthermore, clinical studies show promising results for its use.