Purpose: This study examined how the degrees of muscle activity of Rectus Femoris and Tibialis Anterior during the four phases of walking vary according to three different treadmill slopes of $0^0$, $7^0$, and $15^0$. Methods: Subjects were 14 randomly selected healthy students attending G University in Seoul, Korea who had never had articular problems with lower limb and had no difficulties walking at the time of study. Results: 1) With respect to Rectus Femoris, in every phase of both forward and backward walking, there were significant differences among all of the slope degrees (p <.05), while the activity increased with increased slope degrees in every phase of backward walking. 2) For Tibialis Anterior, only in P2 and P3 of both forward and backward walking there were significant differences in every slope (p <.05). Conclusion: Both Rectus Femoris and Tibialis Anterior were found to be more active during backward walking compared to backward walking. In addition, the activity degree of Rectus Femoris was high between the early part of two foot support phase and the early part of one foot support phase, whereas that of Tibialis Anterior was high between the early part of one foot support phase and the latter part of both foot support phase.