Molar extinction coefficients of radical cations are quantitatively discussed for a variety of substituted polysilanes by nano-second pulse radiolysis. Polysilane solution in benzene under saturated oxygen exhibits a strong absorption band ascribed to polysilane radical cation in the transient spectra. The transient species react with N,N,N',N'-tetramethyl-p-phenylene-diamine (TMPD) to produce TMPD radical cations. Using the molar extinction coefficient of TMPD radical cation, the molar extinction coefficients for the radical cations of polysilanes are found to increase in the range 3.8 x 10(4)-15.0 x 10(4) M-1 cm(-1) with an increase in the segment length of the polymers. This is the first report on the extinction coefficient and oscillator strength of polysilane radical cations. (C) 2003 Elsevier Science B.V. All rights reserved.