Purpose: The objective of this study is to analyze the activities of muscles importantly functioning when walking with different inclinations and speeds of a treadmill, in order to provide basic data on walking exercise using a treadmill. Method: The selected subjects of this study were 16 men and women who had lower extremity injury. A treadmill was used to provide the activation of muscle, and the electromyography was used to analyze the muscle activity variables. The Biodex was used to measure the value of maximum isometric contraction. The inclinations of the treadmill were 0%, 5% and 10%, respectively, and its speeds were 2Km/h. 3Km/h, 4Km/h, 5Km/h, and 6Km/h, respectively. Result: For quadriceps femoris muscle and trunk muscle, there were significant differences in muscle activity when different speeds were applied at 0%, 5% and 10% inclinations.(p<0.05) The activity of vastus medialis muscle was 9.78% at 0% inclination and 2km/h speed, whereas it was 9.32% at 0% inclination and 3km/h, which was slightly lower. The activity of erector spinae muscle was 24.93% at 0% inclination and 2km/h speed, whereas it was 24.84% at 0% inclination and 3km/h, whereas it was 23.99% at 0% inclination and 4km/h, which was slightly lower. The activity of vastus medialis muscle was 11.89% at 10% inclination and 2km/h speed, whereas it was 10.65% at 10% inclination and 3km/h, which was slightly lower. The activity of rectus femoris muscle was 10.26% at 10% inclination and 2km/h speed, whereas it was 9.77% at 10% inclination and 3km/h, which was slightly lower. Conclusion: It was found that the activities of trunk muscle and quadriceps femoris muscle increase as the inclination and the speed of a treadmill increase during treadmill walking.