The electronic structures of five polysilanes and octa(t-butyl)octasilacubane were investigated by ultraviolet photoemission spectroscopy (UPS). The spectral features were assigned by comparison with spectra of the constituents parts. The UPS spectra of the polyalkylsilanes indicate that the valence electronic structure can be regarded as an overlap of those of the Si-backbone and substituents. In the case of polyarylsilanes, all the spectral features except those in the uppermost energy region correspond one by one to each band in the spectra of the substituents as in the case of polalkylsilanes. The deviation of the spectral features in the uppermost energy region from those of the constituents suggests sigma-pi interaction between the pi HOMO states of benzene and the Si sigma HOVB states of the Si backbone. The results of octa(t-butyl) octasilacubane are also discussed.