Sponge-like mesoporous beta-manganese dioxide (β-MnO2) with a high specific surface area and narrow pore size distributions has been successfully synthesized at room temperature by a template-free approach. As a supercapacitor electrode, the as-prepared 3D network β-MnO2 exhibits greatly improved electrochemical performance: not only its specific capacitance enhances from ∼15 F g−1 (traditionally hydrothermal synthesized hollow β-MnO2 nanorods) to ∼180 F g−1 in 1 M Na2SO4 aqueous solutions, but also ∼99% of its initial specific capacitance can retain after charge/discharge for 10000 cycles. In addition, its rate retention can maintain at ∼65% as the scan rate increasing from 2 mV s−1 to 50 mV s−1. These results demonstrate that, through modification or improvement, β-MnO2 can also be a promising electrode material for supercapacitors.