The relation among microstructures, weathering and mass wasting of the Sangun metamorphic rocks in the Kaminishigawa area, Asahi-machi, Okayama Prefecture, was studied. Three stages of penetrative planar structures are recognized; S1 schistosity, S2 crenulation cleavage and S3 crenulation cleavage. The S2 cleavage is the most commonly observed structure. The deree of weathering is divided into two classes on the base of appearance; slightly weathered and highly weathered rock. The three types of mass wasting are also observed in this area; creep, slide and flow type. The S2 cleavage are bent and broken into several blocks in the creep type. The slide type is of rock block sliding along S2 cleavage. The flow type is of debris flow. The type of mass wasting, degree of weathering, and topographic position are mutually related : the slightly weathered rock and creep type are observed on the steep slope at the foot of the mountains; slightly weathered rock and slide type on the steep slope of the mountainside; highly weathered rock and flow type on the gentle slope near the top of the mountains.