Three-dimensional (3D) porous MnO2 array assembled from one-dimensional tubular MnO2 with ultrathin sheets were fabricated by a one-pot hydrothermal method using polycarbonate membrane as the template. The diameter and thickness of nanotubes can be controlled by the membrane. Detailed electrochemical characterization reveals that the porous MnO2 arrays exhibited good rate performance and cycle life. The highest specific capacitance in a three-electrode system was 411.9 F g−1 at a current density of 0.25 A g−1. An asymmetric supercapacitor with porous MnO2 nanotubes arrays as the positive electrode and activated graphene as the negative electrode yielded an energy density of 22.6 Wh kg−1 at a power density of 225.3 W kg−1. The capacitive performance was correlated with the hierarchical structure of the porous MnO2 nanotubes.