The local structures of the two rhombic Ni 3+ centers (on the substitutional and interstitial sites) in rutile (TiO 2 ) are theoretically studied from the perturbation formulas of the g factors for a 3d 7 ion of low spin (S=1/2) in rhombically distorted octahedra. In these formulas, the contributions to the g factors from the low symmetrical parts of the crystal-fields as well as the spin–orbit coupling interaction and orbitals of the ligands are taken into account. From the investigations, the ligand octahedron in the substitutional Ni 3+ center may suffer a slightly larger axial elongation (characterized by the axial distortion angle Δα s ≈−1.09°) than that (ΔαsH≈-0.73°) in the host and the much smaller perpendicular distortion (characterized by the rhombic distortion angle Δθ s ≈−0.75°) than that (ΔθsH≈-9.0°) in the host due to the Jahn–Teller effect. For the interstitial Ni 3+ center, the ligand octahedron is found to undergo a smaller compression (characterized by the axial distortion angle Δα i ≈1.48°) than that (ΔαiH≈8.17°) in the host and a slighter rhombic distortion (Δθ i ≈0.1°) than that (ΔθiH≈7.0°) in the host due to the Jahn–Teller effect. The calculated g factors based on the above structural parameters show better agreement than those based on the host structural parameters and those in absence of the spin–orbit coupling and the orbitals of the ligands with the experimentally observed values.