Trisilanolisobutyl polyhedral oligomeric silsesquioxane (TSI-POSS) with three hydroxyl functional groups pendent to an open cage, was incorporated in concentrations of 7, 13 and 22 wt% into 4,4'-methylenebis(phenyl isocyanate) and glycerol propoxylate to prepare TSI-POSS-PU hybrid composites as a heavy linking node in polymer backbone, respectively. These composites were characterized by FTIR, wide-angle X-ray scattering (WAXS), dynamic mechanical analysis and thermogravimetry techniques. In WAXS profiles, above 22 wt% TSI-POSS concentration, the morphology of composite is significantly altered and distinct crystallite clusters are formed, which increase the volume of hard segment in polyurethane (PU) hybrid composite. As TSI-POSS concentration rises, the glass transition temperature (T (g)) of composites is increased while the decomposition temperature is slightly decreased due to the oxysensitive isobutyl groups in structure. Meanwhile, the activation energy of hybrid composites is nearly unchanged indicating that the formation of crystallite cluster, which restricts motion of surrounding chains, is the predominant effect in T (g) increasing. It can be concluded that the morphology and the thermal property of polyurethane can be tailored by TSI-POSS incorporation, whereas functional group in TSI-POSS structure is the decisive factor for the thermostability of designed composites.