Fabrication of carbon micro/nanostructures by carbon microelectromechanical systems (carbon-MEMS) technique on conductive substrate stably is of great significance but difficulty, for the poor adhesive property and low -temperature resistance of the substrate. In this study, three-dimensional carbon micro/nanostructures are fabricated on stainless steel (SS) substrate for the first time by carbon-MEMS technique and oxygen plasma etching process without extra conductive layer fabrication process. The effects of oxygen plasma etching time and the height of photoresist array on the morphologies of carbon micro/nanostructures are investigated. The carbon micro/nanostructures were then electrodeposited with manganese dioxide (MnO2) thin film as microelectrodes for supercapacitors, and the electrochemical performances of the microelectrodes were demonstrated. At the current density of 0.05 mA cm−2, the MnO2/carbon micro/nanostructures microelectrode deposited with 5 min show a large specific capacitance of 453.47 F g−1. It also shows excellent long-term cycling stability of ∼94% capacitance retention even after 6000 cycling tests. This study shows that the MnO2/carbon micro/nanostructures microelectrodes have great potential for supercapacitors as micro-energy storage devices, and the proposed approach of fabricating carbon hierarchical micro/nanostructures array on a conductive substrate is promising for large-scale micro/nanostructures manufacturing.