Anodic alumina (AAO) templates with different pore sizes were prepared by secondary anodic oxidation method, and then Ni nanowire arrays were grown in AAO templates with different pore sizes by template-assisted electrodeposition method.The morphology, microstructure and composition of the prepared Ni nanowire arrays were characterized by SEM, TEM, XRD and EDS techniques. The magnetic properties of Ni nanowires were investigated by physical property measurement system (PPMS).The results show that the growth mechanism of Ni nanowires is the interaction between the reduction of positive half period Ni2+ by alternating current and the dissolution of negative half period Ni atoms. Ni nanowires have magnetic anisotropy, and with the increase of the diameter, the easy magnetization direction of Ni nanowires gradually changes from parallel to the axis of the nanowire to perpendicular to the axis of the nanowire. The change of easy magnetization direction is caused by the change of the effective anisotropic field and the magnetic domain structure with the diameter of the nanowire.