The reactivity of the alkoxy group in a silane coupling agent toward inorganic surfaces was investigated, and the structure of a silane-treated layer on the particle surface was analyzed. For this purpose, the various inorganic filler particles, SiO2, Al(OH)(3), Mg(OH)(2), Al2O3, and CaCO3 were treated with gamma-mercaptopropyltrimethoxysilane. A strong interaction between the particle surface and the silane due to the hydrogen bonding and ionic interaction was confirmed except for CaCO3 by electron spectroscopy for chemical analysis (ESCA). The structure of the silane layer on the particle surface was affected significantly by both the amount of added silane and the treatment conditions. Different silane structures, such as monolayer- or network-like, were formed on the particle surface. Their influences on the mechanical properties of filled vulcanized rubber were also investigated. The silane-treated filler particles, except CaCO3, showed ability as a semi-reinforcing filler for vulcanized rubber. However, the structure of the silane-layer on the particle surface hardly affected the mechanical properties.