Organic-inorganic hybrid network polymers have been synthesized from cubic silsesquioxane, 1,3,5,7,9,11,13,15-octakis(dimethylsilyloxy)pentacyclo[9,5,1,1,1,1] octasilsesquioxane (POSS) and divinyl or diallyl compounds using hydrosilylation reaction with a Pt catalyst. A hydrosilylation reaction of POSS and 1,5-hexadiene in toluene/methanol mixed solvent induced phase separation and yielded porous polymer composed of connected spheres. Porous hybrid network polymers were also obtained by the reactions of POSS with disubstituted-divinylsilane monomers, divinyldimethylsilane and divinyldiphenylsilane, or 1,4-bis(dimethylvinylsily) benzene. Morphology of the porous polymers in the present research indicates that formation of the porous structure is induced by phase separation via spinodal decomposition.