Monofunctional-anhydride polyhedral oligomeric silsesquioxane (i-C4H9)(7)Si8O12OSi(CH3)(2)(C8H9O3) (AH-POSS) was synthesized and characterized by FTIR, NMR, element analysis. Then AH-POSS was incorporated into epoxy system either pre-reacted or non-reacted using hexahydrophthalic anhydride (HHPA) as curing agent. Pre-reacted system hybrid materials were obtained by two-step preparation. First, AH-POSS reacted with part of diglycidyl ether of bisphenol A (DGEBA) to form AH-POSS-epoxy precursor in DGEBA, then cured with HHPA. Non-reacted POSS/epoxy hybrid materials were prepared by directly mixing AH-POSS. HHPA and DGEBA together and cured afterwards. The GPC and FTIR spectra suggested successful bonding of AH-POSS and epoxy resin. Morphologies of hybrid materials were characterized by SEM and TEM. Non-reacted system led to a dispersion of spherical particles with sizes in the range of micrometers. For pre-reacted system, polymerization-induced phase separation took place with POSS content lower than 30 wt% and also some "vesicle" structure was formed after curing. A typical macro-phase separation happened with POSS content up to 40 wt% before and after curing. The glass transition temperatures (T-g's) and the storage modulus were measured by dynamic mechanical analysis (DMA). T-g's and modulus displayed irregularly decrease. The initial thermal decomposition temperatures (T-d's) characterized by TGA were also irregularly decreasing for both systems. However, they were higher than those of epoxy composites when using amine as the curing agent. (C) 2010 Elsevier B.V. All rights reserved.