Ni nanotube arrays with smaller diameter (around 45 nm) have been fabricated by direct-current electrodeposition into the pores of porous anodic alumina membrane. The crystal structure and micrograph of Ni nanotube arrays were characterized by X-ray diffraction, field-emission scanning electron microscopy. It is found that the diameter of Ni nanotubes is corresponding to the pore size of the porous anodic alumina membrane used in our work. The magnetic hysteresis loops obtained by a Physical Property Measurement System show that the coercivity of Ni nanotubes is smaller than that of Ni nanowires with the same diameter, and larger than that of Ni nanotubes with larger diameter reported in the previous works. The study of Ni nanotubes with small diameter may open up new opportunities for the design and control of nanostructures such as the fabrication of magnetic recording devices. (c) 2008 Published by Elsevier B.V.