In the present study, 100 MeV Si9+ swift heavy ion (SHI) irradiation has been used as a tool to enhance the electrochemical properties of ionic liquid based polymer electrolyte nanocomposite membranes and their fluence dependant properties have been investigated. Polyaniline (PAni) nanofibers have been grown inside the interlayer galleries of montmorillonite (MMT) and used as hybrid nanofiller. With increasing fluence interlayer spacing of MMT increases leading to exfoliation of MMT platelets at the fluence of 5 x 10(11) ions cm(-2) dispersing MMT layers and PAni nanofibers in the polymer matrix as confirmed from HRTEM and XRD studies. DSC results show that the degree of crystallinity decreases with increasing fluence. SEM micrographs reveal that with increasing fluence porosity increases. Contact angle measurements show that SHI irradiation turns the hydrophilic electrolyte membranes to hydrophobic at the fluence of 5 x 10(11) ions cm(-2). Highest room temperature ionic conductivity of 8.4 x 10(-2) S cm(-1) has been obtained for the polymer electrolyte nanocomposite membrane irradiated with the highest fluence of 1 x 10(12) ions cm(-2). Scaling of ac conductivity demonstrates that ion concentration and ion diffusion length change with changing fluence. The nanocomposite electrolyte membranes irradiated with the fluence of 1 x 10(12) ions cm(-2) are electrochemically stable up to 7.1 V. (C) 2015 Elsevier B.V. All rights reserved.