OBJECTIVE The aim of this study was to evaluate the accruing effects of conjugated linoleic acid (CLA) supplementation and aerobic exercise (Ex) on body composition and serum lipid profile in humans. METHODS Forty-four healthy female young subjects were divided ExCLA, CLA, Ex and control (C) groups. The groups of CLA and ExCLA were supplemented with 3.6 g/d CLA whilst ExCLA and Ex groups were exercised for 30 min(-1.)3 days(-1.)week(-1) for 6 weeks. RESULTS After the study period, fat ratio, fat mass, waist and hip girths were reduced in all experimental groups and fat-free mass induced in ExCLA and CLA groups and body weight was reduced in the CLA group when compared to baseline levels. These alterations were significantly different than those of controls with the highest variations were observed in the ExCLA. There was no change in serum leptin, apo-AI, apo-B, total cholesterol, HDL, LDL, free fatty acid, and triglyceride levels. Serum glucose concentrations of ExCLA and CLA groups and insulin level of ExCLA group decreased significantly as compared to baseline levels with only serum glucose reduction of both groups were significantly different than those of controls (P<0.05). Endurance performance significantly increased in ExCLA and Ex groups (P<0.01) but did not vary in the CLA and controls. CONCLUSIONS It was shown that both CLA and exercise were effective in improvement of body composition and these effects were cumulated when they have been used together. CLA supplementation alone or with exercise seems effective on serum glucose and insulin concentrations but ineffective on endurance performance.