Morphological investigations for hybrid materials composed of phenolic resin and silica, prepared by in situ polymerization of silicon alkoxide, were performed using TEM. Irregularly shaped silica particles a few tens of nanometres in size, composed of hyper-fine particles, are homogeneously dispersed in the transparent hybrid materials forming a partial or uniform silica network depending on the silica content. In the translucent hybrid materials, the dispersion of complex silica aggregates (ca. 100 nm) were observed uniformly throughout the sample. In the opaque hybrid materials, silica particles of micrometre range were found to be incorporated uniformly, although the interface was uneven. Such large silica particles embedded in the hybrid material contain both silicon oxide and phenolic resin in an interpenetrating network of both components. It was considered that these different morphologies observed in transparent similar to opaque hybrid materials are caused by freezing-in the silica aggregation at different stages in the course of phase-separation between phenolic resin and silica formed in situ. These morphological characteristics were also compared with those of conventional phenolic resin/silica glass composites.