The degree of electron delocalization along polymer skeletons was discussed for ion radicals of poly[bis(palkylphenyl)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 (n(del)) gave the value of n(del) as similar to36 Si units for excess electrons on poly [bis(p-n-butylphenyl)silane] in contrast to the value of n(del) = 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 similar to2 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(methylphenylsilane), suggesting that the Si skeleton of poly [bis(p-alkylphenyl)silane]s should be good conducting paths for holes.