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(Ni,F)-doped α-Bi2O3 nanomaterials were successfully prepared via a facile hydrothermal reaction route. The well-crystallized nanorods have a diameter of 50–150 nm and a length of 1–2.5 µm. The phase formations were studied via x-ray powder diffraction (XRD) together with structural Rietveld refinements. The incorporations of Ni2+ and F− ions in α-Bi2O3 lattices were discussed in relation to the energy dispersive x-ray analysis, x-ray photoelectron spectroscopy and XRD measurements. The band structure of α-Bi2O3 was greatly modified via Ni2+-, F−-codoping in the lattices, resulting in a red shift of the optical absorption edge and a narrowed band energy from 2.8 eV to 2.46 eV. Compared with the direct-allowed feature of pure α-Bi2O3, the indirect transition was shown in the (Ni,F)-doped sample. The valence band and conduction band of (Ni,F)-doped α-Bi2O3 were the hybridized (Bi6s+O2p+Ni3d) and (Bi6p+Ni3d), respectively. The photocatalytic activities on the photodegradation of rhodamine B were significantly improved in the (Ni,F)-doped sample. The effective photocatalysis was discussed in relation to the improved visible-light response, the modified band structure, and the longer dynamic luminescence decay. The longer recombination between the light-created electrons and holes was verified by the transition lifetimes in (Ni,F)-doped α-Bi2O3 nanorods. The reported hydrothermal synthesis was an advantageous approach to preparing α-Bi2O3; it is simple, has a low reaction temperature, no post-sintering is required, no template or surfactant is necessary, it suitable for large-scale production, it is low cost, etc.