To early assess the impaired renal function in the obese children with non-alcoholic fatty liver disease (NAFLD) and to identify the relationship between NAFLD and impairment of renal function. Three hundred and eighty-six obese children were enrolled and divided into NAFLD group and simple obesity group (control) according to the diagnostic criteria. Clinical biochemical parameters and early impaired renal functions were evaluated and compared. Among all patients 234 obese children aged over 10 y were subdivided into 3 groups: NAFLD combined with metabolic syndrome (NAFLD+MS) group, NAFLD group and simple obesity group (control), and the above indexes were compared among 3 groups. The urinary microalbumin levels in NAFLD, NAFLD+MS (>10y) and NAFLD groups (>10y) were significantly higher than those in controls. Additionally, the positive correlations of urinary microalbumin with systolic pressure, triglyceride and 2h-postprandial blood glucose were found. There is early renal dysfunction in children with NAFLD and those accompanied with MS, which may be associated with hypertension and glucose-lipid metabolic disorder. The results indicate that NAFLD is not only an early sign of early impaired renal function but also an early stage of chronic kidney disease (CKD) in obese children.