Hydrous manganese oxide with amorphous structure is prepared by anodic deposition in manganese acetate solution. The effect of heat treatment (100–700°C) on the material characteristics of the oxides is investigated. The thermal property of the deposited oxide is examined by thermogravimetric and differential thermal analyses. Dehydration, organic-matter decomposition, oxidation and crystallization of the manganese oxide as a function of temperature are examined. Glancing angle X-ray diffraction, scanning electron microscope and X-ray photoelectron spectroscopy are carried out to explore, respectively, the crystal structure, surface morphology and chemical state of the oxide electrodes. It is found that the as-deposited manganese oxide, with an amorphous structure and fibrous feature, is further oxidized and tends to tangle with increasing annealing temperature (below 500°C). When the temperature uses above 500°C, the formation of crystalline oxide is confirmed. Cyclic voltammetry is also performed to evaluate the electrochemical performance of the oxide electrodes annealed at various temperatures. Excellent pseudo-capacitive behaviour of the oxide electrodes is revealed at a low annealing temperature (≤200°C). The cyclic stability of the deposited manganese oxide is significantly improved by introducing proper heat treatment.