Electrochemistry of sigma-pi-conjugated polymers, poly[(hexamethyltrisilanylene)oligo(2,5-thienylene)] has been investigated in acetonitrile by using cyclic voltammetric and spectroelectrochemical techniques. Cyclic voltammograms of these polymers films display generally two pairs of main redox peaks, indicating the doping and dedoping processes of the polymers. The electrochemical oxidation of the polymer films results in their partial decomposition, besides the doping, which is shown by electrochemical quartz crystal microbalance and spectroelectrochemical measurements. The decomposition products are characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, FT-IR, and GPC measurements. It is concluded that the decomposition originates mainly from electrochemical cleavage of silicon-silicon bonds in the polymer chains, and the electrochemical stability of the sigma-pi-conjugated polymers may be improved by decreasing the oligosilanylene block size in the polymer chains.