Solid reaction between ilmenite and solid NaOH is studied. The reaction rate is determined by the diffusion process of NaOH into the spherical reaction product layer of ilmenite particles and the activation energy for diffusion is calculated as av. 25.4 ㎉/㏖. Decomposition of ilmenite by NaOH is proceeded obviously by chemical reaction and DTA experiments show that the activation energy of the decomposition reaction is 13.3 ㎉/㏖, which is the half to that of diffusion. Production of NaFeO₂, Na₂TiO₃, by further chemical reaction with excess NaOH is wnfirmed by X-ray diffraction analysis of the reaction product.