Impedance spectroscopic studies of single phase Nd1 - xSrxFeO3 (0.1 <= x <= 0.5), synthesized by solid state reaction method, have been carried out to investigate the electro active regions, conduction mechanism and origin of colossal dielectric constant in the wide temperature (77-358 K) and frequency (1-1.5 x 10(7) Hz) range. These results show that three electro active regions, i.e., grains, grain boundaries and electrode semiconductor contacts are present in these materials. The conduction mechanism changes from Mott variable range hopping to adiabatic small polaronic hopping with the increase in temperature. Moreover, by increasing the Sr concentration the activation energy of conduction and the temperature at which conduction mechanism changes decrease, while the localization length increases. The permittivity of grains is from 8 to 10 while the high permittivity observed at higher temperatures is extrinsic, due to the formation of different Schottky barriers. (C) 2014 Elsevier Ltd. All rights reserved.