The results of numerical model for a tube furnace reactor were proposed to manufacture ultrafine TiO₂ powders. The model equations such as continuity, energy balance and mass balance equations, and the 0th, 1st, and 2nd moment equations of aerosols were considered. The phenomena such as TiCl₄ reaction rate, TiO₂ nucleation rate and the coagulation, diffusion and thermophoresis of TiO₂ powders were included in the aerosol dynamic equations. It is found that the TiO₂ particle concentration becomes higher, as the furnace temperature decreases and also as the inlet TiCl₄ concentration and the total gas flow rate increase. On the other hand, the TiO₂ particle size increases, as the furnace temperature and the inlet TiCl₄ concentration increase and also as total gas flow rate decreases.