We report the synthesis, phase transformation, and electrical property measurement of single-crystal NiGe and ε-Ni5Ge3 nanowires (NWs). NiGe NWs were spontaneously synthesized by chemical vapor deposition of GeH4 onto a porous Ni substrate without the use of intentional catalysts. The as-grown NWs of the orthorhombic NiGe phase were transformed to the hexagonal ε-Ni5Ge3 phase by thermal annealing induced Ni enrichment. This controllable conversion of germanide phases is desirable for phase-dependent property study and applications, and the observation of novel metastable ε-Ni5Ge3 phase suggests the importance of kinetic factors in such nanophase transformations. Electrical studies reveal that NiGe NWs are highly conductive, with an average resistivity of 35 ± 15 μΩ·cm, while the resistivity of ε-Ni5Ge3 NWs is more than 4 times that of the NiGe phase. NWs of nickel germanides, particularly NiGe, would be useful building blocks for germanium-based nanoelectronic devices.