Objective: To investigate the dynamic posture stability during lateral slop walking in terms of temporal distance parameters of gait cycle and the center of pressure (COP) and compare the differences between the side step and cross step. Materials & Methods: An EVaRT system with nineteen reflective markers, two force plates, and the foot switch sensors were used to measure the body movements, ground reaction forces and temporal parameters, respectively, during lateral walking on an inclined walkway with 5° tilt. Twelve normal subjects participated in this study. The subjects were instructed to walk with right leg leading from the bottom to the top of the slope at the self-selected speed using side step and cross step, respectively. The data were collected for 8 seconds for each trial. Results: Different gait pattern was found in the first and second force plate during the cross-step and the side-step walking. The result indicated that the increasing degree of inclination of the slope would cause the factor of unstable posture. The value of anterior/posterior deviation of the cross-step walking was larger than the side-step walking (P <.05). The maximal shift velocity of COP in the single-right foot stance phase during the side-step walking was much faster than in the cross-step walking (P <.05). The similar result was obtained in the single-left foot stance phase (P <.05). Conclusions: The primary finding of the study is that the cross-step walking is more unstable than the side-step walking. And the forward velocity of the cross-step walking is faster than the side-step walking. If there are unstable factors of cross-step walking concluded, the less smooth gait will be expected.