Alkoxysilyl-functionalized epoxy composites were recently reported to offer the ultra-low thermal expansion properties as low as 3–4 ppm/°C at 85 wt% of silica, not normally achievable with conventional epoxy systems. Understanding the curing mechanism of alkoxysilyl-functionalized epoxies is necessary for future applications, especially in semiconductor packaging. For this purpose, the distinctive chemistry of the alkoxysilyl-functionalized epoxy using imidazole and triphenylphosphine catalysts was studied. The chemistry of alkoxysilyl-functionalized epoxies was investigated using model compounds such as monofunctional epoxy, phenol and monofunctional alkoxysilanes. The extent of reaction and reaction products were determined by NMR spectrometry. It was observed that the alkoxysilyl-functionalized epoxy system shows the unique curing characteristics, different from both (1) ordinary epoxy system and (2) hydrolysable alkoxysilanes. The unique curing characteristics for each catalyst system are explained by suggested mechanisms.