Nanoporous MnOx thin-film electrodes are synthesized using a combination of pulsed laser deposition (PLD) and electrochemical lithiation/delithiation methods. A dense Mn3O4 thin-film deposited by PLD can transform into a nanoporous MnOx thin-film after electrochemical lithiation/delithiation. A nanoporous MnOx thin-film electrode exhibits significantly improved supercapacitive performance compared with an as-deposited Mn3O4 thin-film electrode. A MnOx thin-film finally transforms into a MnO2 thin-film through an electrochemical oxidation process during continuous cyclic voltammetry scanning.