Polymer nanocomposites of epoxies with a novel filler, amino-functional butyltin oxide cage (stannoxane), were prepared and characterized. The nanofiller displays a promising antioxidizing effect, besides mechanical matrix reinforcement. The reinforcement can be assigned to physical interactions among the polymer bonded nanofiller. Moreover, the stannoxane cage undergoes a rearrangement to larger poly amino-functional nano-objects at higher temperatures, which highly reduces its extractability: it is practically not extractable from the nanocomposites in most cases. This, together with the fact that only a few weight percent are needed to achieve an optimal effect, makes it attractive as an antioxidative stabilizer. Epoxy stannoxane nanocomposite synthesis, stannoxane reactivity and dispersion (morphology via TEM and SAXS), as well as the nanofiller effect on mechanical properties (DMTA) and on thermal stability are discussed. A brief comparison is drawn between the stannoxanes and the previously investigated POSS nanofiller.