A sonochemical method has been successfully used in order to incorporate MnO2 nanoparticles inside the pore channels of CMK-3 ordered mesoporous carbon. Modification of the intrachannel surfaces of CMK-3 to make them hydrophilic enables KMnO4 to readily penetrate the pore channels. At the same time, the modification changes the surface reactivity, enabling the formation of MnO2 nanoparticles inside the pores of CMK-3 by the sonochemical reduction of metal ions. The resultant structures were characterized by X-ray diffraction (XRD), nitrogen adsorption, and transmission electron microscopy (TEM). CMK-3 with 20 wt.-% loading of MnO2 inside CMK-3 delivered an improved discharge performance of 223 mA h g(-1) at a relatively high rate of 1 A g(-1). Almost no decrease in specific capacity is observed for the second cycle, and a discharge capacity of more than 165 mA h g(-1) is retained after 100 cycles. This is attributed to the nanometer-sized MnO2 formed inside CMK-3 and the high surface area of the mesopores (3.1 nm) in which the MnO2 nanoparticles are formed.