High-resolution electron energy loss spectroscopy (HREELS) is applied to study film surfaces of two silicon-based polymers having methyl and/or phenyl rings as pendant groups: poly(diphenylsiloxane) and poly(methylphenylsilane). These spectra are compared with those obtained by infrared absorption, Raman scattering, and UV/vis absorption spectroscopy for the polymer bulk. Both vibrational and electronic spectra of these two polymers exhibit common features corresponding to the phenyl pendant group excitations. Positions of peaks appearing in HREELS vibrational spectra correspond well to infrared- and Raman-active modes of the polymer bulk. Electronic losses also correspond to the electronic excited states of phenyl groups cited in the literature. Differences related to secondary emission and accumulation of relaxed electrons are assigned to the electronic structure of the film. The absence of a loss corresponding to the excitation of polysilane chain is related to a trapping mechanism.