Mesoporous manganese oxides (MnO2) microspheres were synthesized by the first chemical deposition of manganese carbonate (MnCO3) precursors at room temperature and followed by the low-temperature calcinations under 300, 350 and 400°C. The obtained MnO2 materials exhibit the Akhtenskite type MnO2 crystalline microstructures and the microspherical morphologies with the diameter of about 1μm. The as-synthesized MnO2 microspheres under 300°C exhibit the largest specific area (240.5m2 g−1) and the optimal mesopore volume (0.231cm3 g−1) than the other two samples under 350 and 400°C (111.4, 106.3m2 g−1; 0.055, 0.021cm3 g−1), which contribute to the optimal electrochemical performances for supercapacitors. Moreover, the as-synthesized MnO2 microspheres under 300°C possess the highest tap density (1.156gcm−3) than the other two samples (1.126, 1.043gcm−3), leading to the more feasibility for practical applications in supercapacitors. The as-fabricated MnO2 electrode exhibits a high specific capacitance (129Fg−1 at 0.25Ag−1) and high-rate capability (68Fg−1 at 4Ag−1). The as-assembled activated carbon (AC)//MnO2 hybrid capacitor exhibits a wide working voltage (1.8V), high power and energy densities (2197Wkg−1 and 12.8Whkg−1 at 4Ag−1), excellent cycling behavior (94.3% capacitance retention after 5000 cycles at 1Ag−1), and excellent capacitance recovery performances under different rates (0.25–4Ag−1) for tested 4500 cycles, indicating the promising prospective of the easily fabricated mesoporous MnO2 microspheres for practical applications in supercapacitors.