Flexible energy storage devices gained lot of substantial research interest in the recent decade as their special features and potential applications in different portable electronic devices such as smart sensors, actuators, mobiles, flexible touch screens and electronic newspapers, etc. Therefore, to develop such devices, the flexible electrode and electrolytes with desired mechanical and electrochemical properties are required. In present article, porous nanostructured MnO2 thin films are prepared directly on flexible stainless steel substrate through chemical bath deposition (CBD) method. Further, flexible all-solid-state thin film symmetric supercapacitors (FASSTF-SSCs) have been fabricated using identical MnO2 electrodes with carboxymethyl cellulose- Na2SO4 (CMC-Na2SO4) gel electrolyte. Our results, demonstrate that 0.7 μm thick FASSTF cell exhibits specific capacitance of 145 F g-1 with specific energy of 16 Wh kg-1 and excellent cycling stability after 2500 cycles. In addition, we have presented demonstration of lighting of two light emitting diodes (LEDs) for 135 s which finally confirms the potential applicability of MnO2 based solid-state symmetric cells for high-performance flexible energy storage devices.