Ostwald ripening under a temperature gradient in binary model alloys is investigated using a quantitative phase-field model. The simulations show that a cube of average radius of a second-phase particle is proportional to time, and the particle size distribution shows self-similarity in a steady state, as with a uniform temperature field. It is found that the growth rate of particles under a temperature gradient is faster than that in the isothermal case, and the steady-state particle size distribution depends on the magnitude of the temperature gradient. Furthermore, the second-phase particles migrate from low temperature regions to high temperature regions when a non-uniform temperature field is applied. The migration velocity of particles, averaged over the whole system, increases with the magnitude of the temperature gradient. On the other hand, the velocity of each particle is not relevant to particle size. Hence, the particle migration is entirely ascribed to the diffusion flux driven by the concentration gradient originating from the temperature dependence of solute solubility.