Acute kidney injury (AKI) is a devastating problem that is commonly associated with worse clinical outcomes in critically ill patients. AKI is an independent risk factor for chronic kidney disease, prolonged hospital stay and increased mortalities. several novel biomarkers have been validated for the early diagnosis of AKI. Some of them recently proved to be more effective than those usually used. Liver-type fatty acid-binding protein (L-FABP), a 14kDa protein in the cytoplasm of human renal proximal tubules and bind free fatty acids in response to renal injury. several studies showed that L-FABP is a promising biomarker of several kidney disease. Cystatin C (Cys-C), a low molecular weight protein produced by all nucleated cells of the body, is filtered through glomeruli, and reabsorbed completely through the proximal renal tubules. Also, plasma cystatin C is independent of several factors such as muscle mass, age and gender. Cys-C is investigated to be a good functional biomarker for diagnosis of AKI.