Our purpose was to compare muscle flexibility and strength for lower extremities in the different groups determined by sport and to investigate the relationship between these parameters. We evaluated a total 62 subjects consisting of 19 swimmers, 23 soccer players and 20 controls with four flexibility tests. Isokinetic muscle evaluation of knee flexors and extensors was carried out for all subjects. All the results were significantly different among the groups without a difference between the athletes. The results showed that there was no significant relationship between the strength and flexibility in the athletes. A relationship between flexibility and strength at 60 degrees/s was also indicated in swimmers and soccer players.