In this study, the effect of adding polysilanes (Mw = 500, PMPS) of polypropylene (PP) on the heat-fusion properties was investigated. Addition of PMPS on the surface of PP films led to an increase in the peeling strength such that the modified films could not be peeled off even under the same conditions for which the PP films without PMPS. This result indicated that the modified film could be heat-fused at a much lower temperature than the neat sample. Upon addition of silicone oil of nearly the same molecular weight as PMPS to the surface of PP films, the peeling strength decreased dramatically and the modified films could not be heat-fused any further than the neat PP samples under the same conditions. From FE-TEM results, the discontinuous boundary of the neat PP films was observed even when they were apparently heat fused completely. As for the PP films added PMPS on the surface of them, however, the boundary at the heat fused surface of PP films was hardly observed, and continuous lamella crystals can be observed. Moreover, from the results of viscoelastic measurement of the PP films added PMPS, it was found that the activation energy of the molecular motion of PP in the heat flow region was 30.9 kJ/mol, which was lower than that of neat PP, 34.9 kJ/mol. This result also supported that PMPS can enhance the molecular motion of PP in the molten state. Furthermore, from the dynamic mechanical properties of the PP films added PMPS, it was found that the intensity of the loss tangent of PP in the amorphous region ( relaxation) increased and the peak temperature of them lowered with the amount of the PMPS. Therefore, it was deduced that PMPS can exist in the amorphous regions of PP, and this result agrees the EDS line profile result of STEM-HAADF observation.