<p>The primary purpose of this research is to analyze slope stability based on the engineering properties of clay minerals in weathered granite or mudstone soils. First, to measure the basic physical properties, sieve, liquid and plastic limit, direct shear, and hydraulic conductivity tests were carried out. X-ray diffraction analysis was conducted to determine the mineralogical characteristics of two different soils. The results indicated that the granite soil contained a significant quantity of kaolinite, while the main mineral of mudstone soil was montmorillonite. A cation-exchange capacity (CEC) test was performed to analyze the chemical properties of the weathered soils. Through an automated soil‒water characteristic curve apparatus, the matric suction of the two soil samples was investigated. In spite of the same physical conditions, differences in hydraulic conductivity, shear strength, and CEC were observed due to the different clay minerals. Based on these differences, stability analysis was conducted and revealed that infiltration was the primary cause of shallow infinite slope failure and that an active failure surface occurred at a deeper location in the granite soil than the mudstone soil.</p>