MnO2/carbon nanowires composites (CNWMn) have been prepared through a simple hydrothermal method using carbon nanowires (CNW) as the both reducing agents and scaffolds for MnO2 growth. The crystalline phase of CNWMn is closely related to the hydrothermal reaction time, which has a profound impact on the electrochemical performance of CNWMn composites. Typically, the CNMWn2 (reaction time is 2 h) exhibits a highest specific capacitance of 465 F g(-1) at the current density of 1 Ag-1 in three-electrode systems. In addition, a two-electrode asymmetric system has also been fabricated using CNWMn2 and porous carbon nanowires (PCNW) as positive and negative electrode, respectively. The asymmetric system presents a maximum energy density of 39.2 Wh kg(-1) at the current density of 0.5 Ag-1, which is much higher than that of traditional sense supercapacitors. Moreover, the asymmetric system exhibits excellent rate capability (high energy density of 24.2 Wh kg(-1) at the current density of 10 A g(-1)) and high cycle stability with only 7% loss of its initial capacitance after 2000 cycles. (C) 2016 Elsevier Ltd. All rights reserved.