We report a comparative study of room temperature ferromagnetism (RTFM) in undoped and Ni-doped TiO2 nanowires synthesized by solvothermal method. Both undoped and Ni-doped TiO2 nanowire samples showed the RTFM with coercive field of ~125 Oe due to intrinsic effect. Interestingly, compared to the doped TiO2 nanowires, the undoped nanowires exhibited the higher saturation magnetization value, indicating surface defects such as Ti3+ and oxygen vacancy play more important role in realizing RTFM than Ni doping. The origin of RTFM in the undoped nanowires can be attributed to the ferromagnetic coupling between Ti3+ ions via F+ center resulting from oxygen vacancy on the nanowire surface. Furthermore, saturation magnetization value of the doped nanowires is increased with increasing the doping concentration due to the enhanced ferromagnetic coupling between Ni2+ ions via F+ center.