Abstract In the present work, effect of Swift Heavy Ion (SHI) irradiation by 90 MeV O 7+ ion with four different fluences on P(VdF − HFP)–(PC + DEC)–LiClO 4-dedoped (insulating) polyaniline (PAni) nanofibers polymer electrolytes have been investigated. The irradiated films have been investigated by ac impedance, XRD, FTIR, DSC and SEM analyses. It has been observed that irradiation with swift heavy ion shows increase in ionic conductivity of the composite gel polymer electrolyte films at lower fluences (≤10 11 ions/cm 2) and decrease at higher fluences (≥10 11 ions/cm 2) as compared to the unirradiated film. Maximum ionic conductivity of 1.2 × 10 − 2 S/cm at room temperature has been found after irradiation with fluence 10 11 ions/cm 2. The increase in ionic conductivity at lower fluences could be attributed to the scissioning of polymer bonds, which leads to larger segmental motion of polymer backbone resulting in faster ionic transport through the polymer matrix. However at higher fluences (≥10 11 ions/cm 2) the polyaniline nanofibers get phase separated out from P(VdF − HFP)–(PC + DEC)–LiClO 4 leading to decrease in ionic conductivity. The phase separation phenomenon has been confirmed by DSC, FTIR and dielectric loss spectra. The surface morphology of the irradiated films has been examined by SEM.