Ordered Co43Ni57 nanowire array has been fabricated in a porous alumina template by alternating current electrodeposition. The as-obtained nanowires exhibit a diameter of about 45 nm and aspect ratio of more than 30. X-ray diffraction indicates that the Co43Ni57 nanowires crystallize in Co (fcc) solid solution with a highly preferential orientation (111). The Co43Ni57 nanowire array has an obvious magnetic anisotropy. However, the magnetic properties of such nanowire arrays exhibited a bad thermal stability at the medium temperature of 200 degrees C.