Chemical weathering indices are used to quantitatively define weathering degree of rocks. Several workers have usually defined chemical weathering indices based on mobile elements or oxides. Therefore, these indices work better where chemical leaching intensively has occurred. In order to determine the degree of chemical change in weathered rocks, it is necessary to determine the amount of elements or oxides in both the weathering product in situ and the chemical product transported away as solution. In this study, a chemical leaching index has been defined as the ratio of CaO+Na2O+MgO+K2O in weathered rock to that in fresh rock. Similarly the ratio of Al2O3+Sigma FeO +TiO2+SiO2 has been defined as the chemical weathering product index. These indices have been applied to the Harsit Granitoid. Because the chemical leaching has intensively occurred during weathering of the Harsit Granitoid, both indices show regular change with the degree of weathering.