The purpose of this study is to prevent a landslide by checking the behavior of slope and stabilizing piles according to reinforcement stages with using field measurement data obtained from the slope reinforced by the slope stability systems. To achieve this goal, first of all, the behavior of the slope was monitored by inclinometers during slope modification. The horizontal deformation of slope gradually increased and then rapidly decreased at a certain depth of sliding surface. It indicates that the sliding surface locates at the certain depth below the ground surface. According to this result, stabilizing piles were designed and installed in this slope. To ensure the stability of the reinforced slope using stabilizing piles, an instrumentation system was installed. The maximum deflection of piles was measured at the pile head and the deformative behavior of pile is similar to a cantilever beam. The maximum bending stress of pile is measured at the soil layer. The pile above the soil layer is subjected to lateral earth pressure due to driving force of the slope, while pile below soil layer is subjected to subgrade reaction against pile deflection. A comparison between the measured and calculated behavior of stabilizing piles was fulfilled, and the behavior of slope and stabilizing piles according to reinforcement stages were observed. As a result of this research, the effect and applicability of stabilizing piles and the behavior of slope and stabilizing piles according to reinforcement stages in large-scale cut slope could be confirmed sufficiently.