Thick composites composed of crystalline manganese dioxide (MnO2) and multiwall carbon nanotubes (MWCNTs) were successfully codeposited onto a graphite substrate from an Mn(AcO)(2) .4H(2)O + MWCNTs solution. The rate/ nucleation mechanism of MnO2 deposition was significantly influenced by the introduction of MWCNTs in the plating baths. The specific capacitance of thick MnO2-MWCNT composites, measured from cyclic voltammetry (CV) or chronopotentiometry (CP) in a potential window of 1.0 V, is monotonously decreased from ca. 160 to 80 F/g with increasing the oxide loading from 1.5 to 4.5 mg/cm(2). The lower specific capacitance of thick MnO2 and MnO2-MWCNTs deposits is reasonably attributed to the relatively poorer utilization of electroactive species as well as the compact structure in comparison with a thin Mn oxide deposit (<1 μm). The capacitive performance of these thick MnO2 deposits in 0.1 M Na2SO4 is significantly improved by the application of electrochemical activation and the introduction of MWCNTs, revealing the promising improvement in the capacity of electrodes. (C) 2004 The Electrochemical Society.