Abstract: Chemical weathering of igneous rocks is principally a process of hydrolysi s, leaching loss of alkali and alkali earth metals, removal of silica and accu mulation of aluminum oxides. Rocks with different weathering degrees should po ssess distinctive chemical compositions,which thus can be used to develop variou s weathering indices. After studying 150 samples from various depths at two site sin Hong Kong, a set of chemical weathering indices is proposed to classify the weathered granitic rocks with different weathering degrees in Hong Kong. The pro posed chemical classification system provides not only a theoretical basis for i nvestigating the influence of weathering on engineering properties of weathered rocks, but also a scientific and reliable approach to classify the rocks with d ifferent degrees of weathering.