A novel tin-based FOSS analogue, butylstannoxane dodecamer, was incorporated into epoxy networks with strongly different mesh sizes in comparison to the nanofiller dimensions. The stannoxane cage is especially attractive due to its anti-oxidative effect, which is based on oxidative crosslinking reactions. It can also cause additional reinforcement via nanofiller units' oligomerization. The strongest mechanical reinforcement was observed in nanocomposites with a network mesh width close, but somewhat larger, than was the stannoxane cage size. In the narrow-mesh-matrix, the large rigid nanofiller causes a plastification, due to sterical impossibility of formation of some crosslinks around the filler units. The strongest anti-oxidative effect of the stannoxane was observed in the matrix with the widest mesh, which had the longest polypropylene oxide chains, and hence the largest number of sites potentially reacting with the stannoxane in oxidative crosslinking reactions. The homogeneity of the prepared nanocomposites was evaluated by TEM.