The synthesis of silsesquioxane oligomers containing amino and phenyl groups by solgel process and the formation of an organicinorganic hybrid, by the reaction of amino groups of the silsesquioxane precursor with epoxy rings of diglycidyl ether of bisphenol A, have been investigated. Acid catalysis proved to be more efficient than basic catalysis for the condensation reaction between 3-aminopropyltriethoxysilane (APES) and phenyltriethoxysilane (PETS) in ethanol. Liquid state 29Si nuclear magnetic resonance (29Si NMR) analysis indicated that T3 structures are the major phase forming the network structure. Infrared spectroscopy analyses confirmed the formation of the epoxy/silsesquioxane hybrid and showed that a high degree of cure was achieved. A distinct behavior of the glass transition temperature (Tg) between the hybrids cured at different time intervals after the chemical modification was observed, and the most significant value was an increase of 13 degrees C in Tg obtained with the hybrid produced with silsesquioxane oligomers synthesized by solgel for 18 h. From thermogravimetric analyses (TGAs), it was observed an increase on the residual masses for the hybrids and a decrease in their degradation rates, suggesting an improvement of thermal stability. These results indicate the formation of a new organicinorganic hybrid material with potential applications for high performance coatings and structural components. POLYM. ENG. SCI., 2012. (C) 2011 Society of Plastics Engineers