We report synthesis of vertical Ni3Co nanowires on a c-plane sapphire substrate by chemical vapor transport method. A vapor−solid−solid mechanism was proposed for Ni3Co nanowire growth, which was catalyzed by Ni3Co2 nanoparticle at the tip. As-synthesized vertically aligned single-crystalline Ni3Co nanowires exhibit strongly ferromagnetic properties. Such single-crystalline ferromagnetic alloy nanowires could be important in the application of spintronics such as nonvolatile memory devices. We could also control the composition of the nanowire by adjusting experimental conditions, producing Ni, Ni3Co, and NiCo nanowires.