Epoxy-amine networks were modified with well-defined inorganic building blocks-polyhedral oligomeric silsesquioxanes (POSS). POSS molecules were incorporated in the organic-inorganic networks as dangling units of a network chain or as network junctions. Mono- or polyepoxide POSS monomers were used to prepare the two types of networks. The structure of the POSS-containing networks, including the structure evolution during network formation, was determined by SAXS, WAXS, and TEM. The POSS pendant on a network chain shows a strong tendency toward aggregation and crystallization, depending on the POSS organic ligands. During network formation, ordering of the crystal domains takes place. The POSS-POSS interaction is the main factor controlling the network structure. Also, the polyepoxy POSSs monomers aggregate in the organic matrix; however, during network formation the system becomes more homogeneous and POSSs as network cross-links become better dispersed. Still, in the cured organic-inorganic networks the POSS junctions are slightly aggregated, and the extent of aggregation increases with decreasing POSS cross-link functionality.