Background: The purpose of our experimental study, we want to know a correlation study using the sonogram between the muscle strength and the diameter of Biceps brachii muscle by gender. So we set to hypothesis that Biceps brachii contracted maximally would be a diameter of the muscles increased according to the muscle strength will be increased. Methods: In this study, we measured the muscle strength of biceps brachii on contracting its maximum using the Biodex and the diameter of the muscles using Myo-Lab (25Gold). We experimented 30 subjects of twenty-aged men and women. The subjects is comprised of a persons who has not external injuries and pain of elbow joint, no mobility limitation of ROM, no experiences of surgery in past history. Result: We found that the men have a highly correlation between maximum strength and the diameter of the muscles more than women (p<.05). Conclusion: The results of our experimental study between the muscle diameter and the muscle strength to biceps brachii on relaxation and contraction is a statistically significant relation (r=.394), especially in rather men then women (p<.05). So this results would be based data for further clinical muscle efficiency application in physical therapy field.