This paper studies the preparation and characterization of polyimide (PI)-based porous nano-fibers as separator for supercapacitor. PI-based porous nano-fibers were fabricated by electrospinning soluble PI and polyvinyl pyrrolidone (PVP), followed by solution induced phase separation process under ultrasonic-assisted vibration. The morphology and structure of PI-based separator was investigated by means of scanning electronics microscope, pore structure and specific surface area analysis. The electrochemical performances were characterized by alternative current impedance, cyclic voltammetry and constant current charge/discharge test in an ionic liquid electrolyte. The results indicate that PI nano-fibers derived from PI: PVP mass ratio = 1: 1 electrospun fibers exhibit high specific surface area (212.4 m 2 g −1 ), wide stability electrochemical windows (0.0–4.55 V) and high electrolyte uptake (430 wt . %). The graphical abstract is about the tittle Application of electrospun polyimide-based porous nano-fibers separators in ionic liquid electrolyte for electrical double-layer capacitors. • PI-based porous nano-fibers were prepared via PI/PVP blended electrospinning and solvent induce phase separation process. • PI-based nano-fibers are suitable for the adsorption, diffusion and infiltration of ionic liquids with a large ionic size. • PI-based porous nano-fibers separators exhibit high electrolyte uptake (430 wt %), wide stability electrochemical window (0.0 V–4.55 V) in ionic liquids electrolyte.