Liquid-crystalline (LC) silsesquioxanes having various mesogenic moieties were synthesized by hydrosilylation reaction of octa(hydridosilsesquioxane) and terminal alkenes with mesogenic groups using hexachloroplatinic acid as a catalyst. The obtained LC silsesquioxanes were characterized by FT-IR,H-1-,Si-29-NMR. From the results of differential scanning calorimetry (DSC) and optical polarizing microscopy, their liquid crystallinities of nematic phase were found to be much more stable than those of the corresponding mesogenic compounds due to the effect of the inorganic part which is polyhedral hydridosiloxane core. It was also found that the thermal stabilities of LC silsesquioxanes were improved after hydrosilylation reaction through a thermogravimetric analysis (TGA).