Plasma adiponectin levels are reduced in middle-aged obesity and in patients with type 2 diabetes and coronary artery disease. The purpose of this study was to investigate the effects of early-aged obesity on plasma adiponectin level. Twenty-six male college students (19.2 ± 1.1 years, obese group: n = 15, [body mass index > 25, percent body fat > 25%], non-obese group: n = 11) participated in the present study. We measured anthropometric parameters and plasma adiponectin and leptin level. Plasma adiponectin levels in the obese group were significantly lower than those in the non-obese group (obese: 4.7 ± 2.0 μg/ml, non-obese: 6.8 ± 2.2 μg/ml, p < 0.05). On the other hand, plasma leptin levels in the obese group were significantly higher than those in the non-obese group (obese: 8.4 ± 3.2 ng/ml, non-obese: 2.6 ± 2.1 ng/ml, p < 0.001). Plasma adiponectin levels were significantly correlated with body weight (r = − 0.415, p < 0.05) and percent body fat (r = − 0.412, p < 0.05). Stepwise multiple regression analysis revealed that percent body fat was a significant independent predictor of plasma adiponectin level (r = 0.406, p < 0.05). These results show that obesity is associated with reduced plasma adiponectin even in young subjects.