ZnO nanowires were synthesized by a hydrothermal route without any substrate or template. Structure analyses through XRD, SEM, TEM and HRTEM indicated that ZnO nanowires had high purity and perfect crystallinity, and grew along [0001]. The diameter was 50–80nm, the length was about several micrometers and length-diameter ratio was more than 100. As electrode materials of Ni/Zn batteries, ZnO nanowires showed the obviously improved cycle stability, average discharge capacity of 609mAhg−1, higher discharge voltage/lower charge voltage. Slow rate cyclic voltammetry showed that electrochemical activity of ZnO nanowires was superior to that of the conventional ZnO. The improvements of electrochemical performance were ascribed to the unique nanowire structure. During the charging/discharging cycles, nanowires were broke, grew in diameter, and changed into nanorods. Nanowires lying parallel to the anodes could suppress the growth of dendrite clusters perpendicular to the anodes.