Abstract: AIM To investigate preprandial and postprandial changes of circulating ghrelin and obestatin levels in simple obesities. METHODS Plasma ghrelin and obestatin concentrations 1 hour before meal were measured by radioimmunoassay in 16 simple obese adolescents and 14 normal controls. Body mass index, waist-hip ratio, plasma glucose, plasma insulin, blood lipids, white blood cells count and high sensitive C-reactive protein were measured. Plasma ghrelin and obestatin concentrations 2 hours after meal were measured in 10 of the simple obese adolescents and 10 of the controls. RESULTS Although both prepramdial plasma ghrelin (P<0.01) and obestatin (P<0.05) concentrations decreased in simple obesities as compared with those in normal controls (both P<0.01), their ratios of ghrelin to obestatin were increased (P<0.01) even after adjustment for gender and age. The ratios of postprandial ghrelin to postprandial obestatin decreased both in simple obesities (P<0.05) and normal controls (P<0.01) compared with their preprandial ratios, but the postprandial ratios were similar between simple obesities and normal controls. There were significant positive correlations respectively between prepramdial ghrelin/obestatin and BMI (r=0.54, P<0.01), waist circumference (r=0.39, P<0.05), total cholesterol (r=0.40, P<0.05), low-density lipoprotein cholesterol (r=0.41, P<0.05). CONCLUSION The imbalance of prepramdial circulating ghrelin and obestatin may play a role in the pathogenesis of human obesity.