In this paper, we report the effect of different plasticizers, such as poly ethylene glycol, propylene carbonate, ethylene carbonate and dimethyl carbonate on the ionic conductivity and dielectric relaxation of PEO-LiClO4 solid polymer electrolytes. The highest ionic conductivity is obtained for polymer electrolyte plasticized with poly ethylene glycol. The temperature dependence of ionic conductivity follows the well known Vogel-Tamman-Fulcher relation which indicates a strong coupling of ionic and segmental motions for all compositions. The experimental data for the complex dielectric permittivity and electric modulus have been studied using Havriliak-Negami function for the understanding of ion dynamics. Maximum dielectric strength is obtained for polymer electrolyte plasticized with poly ethylene glycol. The modulus data have been analyzed using non-exponential Kohlrausch-WilliamsWatts (KWW) function. It is observed that the non-exponential parameter beta is quite lower than unity, suggesting highly a non-exponential relaxation exists in these materials. The temperature dependence of relaxation times obtained from dielectric and modulus formalisms also follow Vogel-Tamman-Fulcher relation for all plasticizers in the compositions. (C) 2015 Elsevier Ltd. All rights reserved.