Nano-sized epoxy oligosiloxanes (EO) were prepared by condensation reaction between 3-glycidoxypropyltrimethoxysilane (GPTS) and Diphenylsilandiol (DPSD). Through a composition change of GPTS and DPSD, EO of various structure and sizes were obtained. The molecular structure and size of EO synthesized were investigated by experimental measurements. Regardless of their composition, molecular structure of EO was linear or branch. The amount of species of high molecular weight and their molecular size increased with addition of DPSD. We confirmed that epoxy groups of EO were thermally cured using a thermal initiator and curing agent. Finally, we fabricated transparent epoxy-based hybrimer films by thermal curing of EO resins. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 756-763, 2009