Background: The present study was conducted to investigate the possible effects of L-carnitine and glutamine and their synergistic effects on male soccer athletes. Methods: 28 male soccer players (21.1 ± 0.7 y) were enrolled in a randomized pre and post intervention, double-blind design. Before the intervention, their performances were assessed by Bruce protocol, and their body composition was measured with the body composition analyzer. Then, athletes were randomly allocated into four groups: 2 g L-glutamine, 2 g L-carnitine, 2 g L-carnitine + 2 g L-glutamine and placebo. Supplements were prescribed for 21 days and after three weeks, athletes' performances and body composition were re-evaluated. Results: The results showed that body weight, body fat percentage, lean muscle mass, and dietary intake made no significant changes in different groups of athletes. In between groups comparison, results did not significantly change in any performance indices. However, in L-carnitine supplement group, the results of pre and post intervention showed that the running distance and maximal oxygen uptake (VO2max) increased significantly while the subjective sense of fatigue decreased significantly. Conclusions: Based on our findings, a three-week prescription of separateor combined glutamine and L-carnitine, had no effects on body composition or dietary intake in soccer players. But, the athletes' energy intake was more than the one reported in other studies. Although further studies are required to assess these effects on athletic performance.