MnOOH nanowire-graphene oxide composites are prepared by hydrothermal reaction in distilled water or 5% ammonia aqueous solution at 130 degrees C with MnO2-graphene oxide composites which are synthesized by a redox reaction between KMnO4 and graphene oxide. Powder X-ray diffraction (XRD) analyses and energy dispersive X-ray analyses (EDAX) show MnO2 is deoxidized to MnOOH on graphene oxide through hydrothermal reaction without any extra reductants. The electrochemical capacitance of MnOOH nanowire-graphene oxide composites prepared in 5% ammonia aqueous solution is 76 F g(-1) at current density of 0.1 A g(-1). Moreover, electrochemical impedance spectroscopy (EIS) suggests the electrochemical resistance of MnOOH nanowire-graphene oxide composites is reduced when hydrothermal reaction is conducted in ammonia aqueous solution. The relationship between the electrochemical capacitance and the structure of MnOOH nanowire-graphene oxide composites is characterized by cyclic voltammetry (CV) and field emission scanning electron microscopy (FESEM). The results indicate the electrochemical performance of MnOOH nanowire-graphene oxide composites strongly depends on their morphology. (C) 2011 Elsevier Ltd. All rights reserved.