In the initial stage of the hydrolysis–condensation of tetraethoxysilane (TEOS), hexaethoxydisiloxane (HEDS) and octaethoxytrisiloxane (OETS) are formed. However, little is known about the hydrolysis–condensation of HEDS and OETS. In this study, the hydrolysis–condensation of TEOS, HEDS, and OETS was investigated. HEDS and OETS were synthesized from diethoxy(diisocyanato)silane, a raw material with controllable functionality. The hydrolysis of TEOS, HEDS, and OETS was analyzed by mass spectroscopy, gel permeation chromatography, and nuclear magnetic resonance. The hydrolysis–condensation product of TEOS was a three-dimensional network-type polysiloxane. The hydrolysis–condensation product of HEDS consisted mainly of four-membered cyclic siloxane. The hydrolysis–condensation product of OETS consisted mainly of various membered cyclic siloxanes.Graphical Abstract