The organic-inorganic (O-I) hybrid networks were prepared from two types of O-I precursors: (a) alkoxysilane-end-capped oligomers (ASO) and U epoxy-functional silsesquioxane (SSQO) clusters (EC). ASO precursors were cross-linked by hydrolysis and condensation of alkoxysilane groups and the EC by the reaction of the epoxy groups with oligomeric diamine. Structure evolution and formation of the networks were followed by NMR, SAXS, and chemorheology. In addition, nongelling model systems were used to analyze the structure. Gelation mechanism and effects governing the structure evolution are discussed. Depending on catalysis of ASO polymerization, the compact SSQO cagelike structures or loose SSQO clusters are formed at the chain ends, serving as junction domains of the O-I network. In the EC-amine system, large SSQO cylinder-like domains are produced and interlinked with diamine chains. Decreasing the size or a content of the oligomeric amine results in percolation of the SSQO structure. During cross-linking a structure ordering occurs.