The degree of electron delocalization along polymer skeletons was discussed for ion radicals of poly[bis(p-alkylphenyl)silane]s by electron beam pulse radiolysis. The degree of delocalization of negative charges on the Si chains strongly depended on the substitution position of the alkyl groups (n- and tert-butyl) on the phenyl rings, though relatively small effects were observed for holes. The empirical relationship between oscillator strength and the degree of delocalization (ndel) gave the value of ndel as ∼36 Si units for excess electrons on poly[bis(p-n-butylphenyl)silane] in contrast to the value of ndel = 14 for poly[bis(p-t-butylphenyl)silane], which was similar to that for poly(methylphenylsilane). The oscillator strength of the cation radicals of poly[bis(p-alkylphenyl)silane]s (f•+ > 0.65) was ∼2 times higher than that of poly(methylphenylsilane) (f•+ = 0.35). Positive charges gave a higher degree of delocalization in poly[bis(p-alkylphenyl)silane]s in comparison with that in poly(methylphenyls...