Poly (vinylidene fluoride) (PVdF) ultrafine porous fiber membranes with a three-dimensional network structure, high porosity and electrolyte uptake are prepared via a blend electrospinning and phase separation process under ultrasonic-assisted vibration. The structure and morphology of PVdF fiber membranes are investigated by the scanning electron microscope and porous structure parameter analyzer. The electrochemical performances of supercapacitor constructed with PVdF ultrafine porous fiber membrane as separator-cum-electrolyte are investigated. PVdF ultrafine porous fiber membranes possess high electrolyte uptake (360 wt%) and wide electrochemical stability windows (0.0 to 3.3 V). The activated electrode supercapacitor constructed by PVdF ultrafine porous fiber separator-cum-lectrolyte exhibits superior specific capacity (39.5 F . g(-1)) even under high current density (100 mA . g(-1)). (c) The Author(s) 2017. Published by ECS. All rights reserved.