MnOOH nanowire–graphene oxide composites are prepared by hydrothermal reaction in distilled water or 5% ammonia aqueous solution at 130°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 76Fg−1 at current density of 0.1Ag−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.