Epoxy resins have been used extensively as the dielectric and the mechanical support in solid insulation systems, such as electrical machines. Recently, thanks to the development of nanotechnology, epoxy nanocomposites have been expected to be potential candidates to replace the base resin. However, the effects of nano-fillers have been controversial, in both positive and negative ways. It is believed that the properties of nanocomposites are related to the surface chemistry of nano-fillers. The incorporation of nano-fillers with large interfacial areas into epoxy matrices may also modify the cure behaviour of the system, through introducing additional chemical reactions between moieties on the nano-filler surfaces and reactants thereby change the chemical balance of the original system. This project sets out to investigate the effects of stoichiometry and the nature of the interfacial areas of treated silica particles of various sizes on the properties of an epoxy-based system, and hence, provide a more comprehensive insight into the relationships between formulating reactants and incorporating fillers with the formed molecular architecture, which is associated with the end properties of products.