A high-performance supercapacitor electrode consisting of platelet ordered mesoporous carbon CMK-5 and polyaniline (PANi) was prepared by chemical oxidative polymerization of aniline in the presence of CMK-5. The PANi with uniform size of 2-5 nm was primarily confined in the mesochannels of CMK-5 at low PANi loadings (40 and 51 wt %), whereas at a high loading of 64 wt %, additional PANi thin films with thicknesses of 5-10 nm were coated on the surface of the CMK-5 particles. Such CMK-5-PANi composites afforded a high electrochemical active surface area for surface Faradic redox reactions, leading to a more than 50% utilization efficiency when considering the theoretical capacitance of PANi of about 2000 F/g. As a result, a specific capacitance of 803 F/g and an energy density of 27.4 Wh/kg were achieved for CMK-5-PANi composite electrode with 64 wt % PANi, showing substantial improvement as compared with symmetric capacitors configured with CMK-5 electrodes (10.1 Wh/kg) or pure PANi electrodes (16.4 Wh/kg). Moreover, an excellent rate capability and a substantially enhanced electrochemical stability with 81% capacitance retention as compared with 68% of pure PANi were also observed over 1000 charge-discharge cycles at a constant current density of 4.0 A/g.