Dielectric relaxation of chlorinated polyvinyl chloride stabilized with di-n-octyltin maleate has been studied in the frequency range 1 kHz-1 MHz at various temperatures between 300 and 450 K. A clear dielectric relaxation band (alpha-type) associated with dipolar polarization has been observed in the studied range. The stabilizer molecules increase the segmental mobility of the polymer, and specific interaction occurs between both the C-Cl and C=O polar groups. The temperature dependence of the relaxation process was analyzed by combining the critical free volume expression by Cohen and Turnbull with the Williams-Landel-Ferry (WLF) model of the thermal expansion of free and Occupied volumes. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 316-320, 2009