Purpose : This research was conducted to see the correlation between sway speed and muscle activity for lower extremity of stroke patients through unstable surface training. Methods : A total of 60 patients were randomly divided unstable surface group (30 peoples) and stable surface group (30 people). Then they were asked to carry out the same exercise program for 6 weeks. The unstable surface group and stable surface group performed the exercise program on the balance mat and on the hard wood block. We checked the changes of sway speed and the changes in muscle activity for lower extremity. Results : The unstable surface group displayed significantly reduced sway speed, and improved muscle activity of lower extremity. There were significant correlation between change amount of muscle activity and sway velocity in Gastrocnemius, Biceps femoris during unstable surface training(r=.373, p<.05)(r=.369, p<.05). And there were not show significant differences during stable surface training. Conclusion : Judging from this, we can have knowledge that the correlation between increase of muscle activity and decrease of sway velocity for Gastrocnemius, Biceps femoris in the unstable surface training.