This Study was to discuss the necessity of strength on modern dance, and the recognition the important factors of how to manifest the largest muscle power of leg for modern dancer. 7males with no fisk symptoms of respiratory system was selected out of a group of modern dancers through the physical load test, and the isokinetic training and measurement for subjects was performed with Cybex for 60?sec of the typical load of strength, for 120?sec of the typical load of agility, 180?sec of the typical load muscle-endurance, and the load was changed in 20 minute cycle. The protocol of measurement was performed in 3 times of each, 3 times of each, and 30 times of each during 8 weeks. The results of this study were as follows.First, there was a significant increase of an extensor and flexor with 60?sec, 120?sec, 180?sec on an efficiency of maximum strength. Second, there was no significant increase of an extensor and flexor with 60?sec, 120?sec, 180? on an average power.I would like to suggest problems and research task which is discovered form this study. Recently, the research about the effect of Iso-kinetic training in dance fields in quitely much insufficient than the sports fields. Iso-kinetic training is an efficient program, for reinforcement of strength in not only modern dance but also korea traditional dance and ballet, so that the intensive research is required.