Catalytic effects on the water-cross-linking process (hydrolysis and condensation) of vinyltrimethoxysilane-grafted ethylene-propylene copolymer (EPR-g-VTMS) were investigated for several amine compounds (primary, secondary, and tertiary). Silane water-cross-linking kinetics and curability of EPR-g-VTMS samples containing each specific amine were analyzed by the ATR-FTIR technique and gel-fraction method using xylene as an eluent. The primary amine showed the strongest catalytic effect, followed by the secondary one. The tertiary amine, meanwhile, showed little catalytic effect. Moreover, the amine compound with a small substituent had a much faster initial rate of the silane water-cross-linking reaction than the one with a large substituent. In order to gain visual insights into the hydrolysis and condensation of an alkoxysilane in the presence of the amine compound, the plausible reaction intermediates were examined using a semiempirical molecular orbital method (AMI level) for each case. The novel possible catalytic mechanism for the amine compounds in the EPR-g-VTMS system is proposed on the basis of these results and the knowledge of traditional silicate sol-gel reactions.