Background: The purpose of this study was to investigate (1) the association among anthropometric measurements, cardiopulmonary fitness, liver enzymes and inflammatory markers including vaspin levels among male adolescents, and (2) the effects of a 12 week aerobic exercise training on insulin resistance, liver enzymes and inflammatory markers including vaspin levels among obese male adolescents were also studied. Methods: We compared anthropometric and metabolic parameters between thirty obese (BMI ≧ 25) and fifteen lean (BMI < 23) male high school students (17.0 ± 0.1 y). Obese male subjects were randomly assigned to either exercise intervention group (OIG, n = 18) or control group (OCG, n = 12). OIG participated in aerobic exercise (5 days/wk) for 12 weeks, while the OCG participated only in regular physical education class. Results: Partial correlation coefficient analysis showed no association between vaspin levels and metabolic parameters including insulin resistance. However, vaspin levels have significantly correlated with intima-media thickness (IMT). Parameters which were significantly associated with insulin resistance were gamma- glutamyltransferase (GGT) and VO2max, while adiponectin levels showed significant association with VO2max and fasting insulin levels. Twelve weeks of exercise training significantly improved insulin resistance with concurrent improvement in adiponectin and GGT without affecting the vaspin levels. Conclusion: Our findings suggest that 12 week of aerobic exercise training significantly improved insulin resistance and metabolic parameters. However, it did not affecting the plasma vaspin levels.