The free radical copolymerization of vinyl imidazole (VI) with gamma-methacryloxypropyltrimethoxy silane (gamma-MPS) by using azobisisobutyronitrile (AIBN) as an initiator was carried out in benzene at 68 degrees C. The copolymer compositions at various monomer feeds were investigated by elemental analysis. The reactivity ratios of two monomers were determined by the Finemann-Ross method : r(1)(VI) = 0.22, r(2)(gamma-MPS) = 3.18. From these results, it could be concluded that silane-modified polyvinylimidazoles were random copolymers (0 < r(1)r(2) < 1). Thermal stability of the copolymer increased with increasing the mole ratio of VI in the copolymer. Thermal decomposition of the copolymer was caused by the decomposition of the gamma-MPS unit. However, thermal stability above 300 degrees C and maximum thermal decomposition temperature increased with increasing the mole ratio of gamma-MPS due to the crosslinking reaction of hydrolyzed gamma-MPS unit.