We have prepared two polysiloxane networks with different molecular structures and similar compositions as suitable precursors of silicon oxycarbide glasses (SiOC), in order to understand the influence of the molecular architecture of the polymeric networks on the structure of these glasses. The structural evolution from the polymeric precursor to glasses was followed by solid-state Si-29 magic angle spinning nuclear magnetic resonance (Si-29 MAS NMR) and FTIR spectroscopies, X-ray diffraction, thermogravimetric analysis, and density measurements up to 1000 A degrees C. The high- temperature behavior of SiOC glasses, up to 1600 A degrees C, was studied by X-ray diffraction, and Si-29 MAS NMR spectroscopy. The formation of carbosilane bridges in the polymeric networks during the hydrosilylation reaction contributed to the generation of a larger amount of carbidic sites in the final products. An increase in the pyrolysis temperature led to a distribution of silicon sites and crystallization profiles that depended on the molecular architecture of the polymeric precursors.