An ultraviolet photoelectron spectroscopic study was performed to examine the electronic structure of poly-(1,1,2,2-tetramethyldisilylenemethylene), [(SiMe2)(2)CH](n), which consists of repeating Si-Si-C units. We compared the observed spectra to reported gas-phase spectra of Si2Me6 and Si4Me10 and theoretical molecular orbital calculations. Theoretical calculations by the ab initio and PM3 methods agree well with the observed spectra, which enabled assignment of the observed spectral features. The broad peak derived from Si-Si bond orbitals in polycarbosilane suggests that Si-Si units, which are separated by carbon atoms, still interact with each other, to form sigma -conjugation through the backbone. The observed ionization threshold energy of the polycarbosilane[(SiMe2)(2)CH2](n), is 6.4 eV. The dispersion of the highest valence band of polycarbosilane is less than that of polysilane, indicating that the degree of sigma -conjugation of polycarbosilane is smaller than that of polysilane.