The aim of this study was to determine the effect of 6 weeks of aerobic training and L-carnitine supplement on body fat percent and serum lipid profiles in active men. The method used was semi-experimental. Eighteen active men were selected voluntarily and randomly divided into two groups of experimental (nine individuals with the average age: 44.4+8 years, weight: 8.2+16.6 kg, height: 173+6 cm, BMI: 26.9+4.8 kg/m2) and control (nine individuals with the average age: 48.8+8 years, weight: 82.8+9.5 kg, height: 169+0.05 cm, BMI: 29+3.8 kg/m2). Both groups performed aerobic training based on the principle of overload for 6 weeks. During this period, the experimental group consumed 10 mg/kg/day L-carnitine orally (average less than 1 gram/day) and control group ingested 2.5 mg/kg/day B1 vitamin as placebo. Before and after aerobic training, blood samples were gathered. In addition, aerobic power and body composition were measured. The data were analyzed using Kolmogorov Smirnov, paired, independent t test and ANCOVA. The results showed that aerobic training and L-Carnitine supplement significantly reduced body fat percent (P<0.05), but they had no significant effect on serum triglyceride, total cholesterol, LDL-C and HDL-C. We concluded that if middle age men would like to reduce their body fat percent, they can use L-carnitine supplement with low dosage along with aerobic training. However, determining positive effects of aerobic training and L-carnitine supplement on serum lipid profiles needs further investigation.