ABSTRACT: The purpose of this study is to investigate the effect of mechanical properties of the impact material, and the shape of boulders on the coefficients of restitution. Four slope platforms with different Young's modulus (granite, shotcrete, plaster and soil) were used in this study. Four different shapes of boulders: spherical, cylinder, hexagonal prism and cube are prepared. Images of each test are captured by using a high-speed camera. Based on the experimental study, it is found that the coefficients of restitution are strongly affected by the elastic modulus of the material of the platform and the shape of boulder. A slope with smaller value of Young's modulus is conducive to permanent deformation during the impact, and, consequently, lower coefficients of restitution will be resulted. For the shape effect of boulders, a more angular boulder, will lead to lower rebound amplitude with rotation. With this induced rotation, the normal rebound velocity is reduced but the tangential velocity is increased. Three empirical formulas are proposed for Rn estimation under the various modulus an different shapes of boulder.