In present work,the vertically aligned NiS nano-flakes composed thin film is prepared by anionic exchange process in which hydrothermally prepared Ni(OH)2 is used as a parent thin film and Na2S as a sulfide ion source.This synthesis process produced fully transformed and shape-controlled nano-flakes of NiS from nano-flowers of Ni(OH)2.The electrochemical supercapacitor properties of NiS electrode are studied with cyclic voltammetry (CV),galvonostatic charge discharge (GCD) and electrochemicalimpedance spectroscopy (EIS) techniques.Highly porous surface area (85 m2/g) of NiS nano-flakes makes large material contribution in electrochemical reaction stretching specific capacitance (C5) of 880 F/g at scan rate of 5 mV/s and 90％ electrochemical stability up to 4000 CV cycles in 2 M KOH electrolyte.Further.the flexible solid-state symmetric supercapacitor device (NiS/PVA-LiClO4/NiS) has been fabricated using NiS electrodes with polyvinyl alcohol (PVA)-lithium perchlorate (LiClO4) gel electrolyte.The NiS/PVA-LiClO4/NiS device exhibits specific capacitance of 56 F/g with specific energy of 14.98 Wh/kg and excellent cycling stability after 2000 cycles.In addition,the NiS/PVA-LiClO4/NiS device demonstrates illumination of red light emitting diode (LED) for 60 s.which confirms the practical applicability of NiS/PVA-LiClO4/NiS device in energy storage.