We propose a new method for determination of interdiffusion coefficient in high temperature solutions. This method can be characterized by the three following facts: the flux of diffusion is temporarily measured by in situ measurement technique for solution concentration in a diffusion cell; the intrinsic diffusion coefficient is derived from the flux on a basis of Fick's first law; the interdiffusion coefficients are evaluated from the intrinsic diffusion coefficients. In practice, the interdiffusion coefficient of GaZn binary system was successfully determined using the present method. (C) 2002 Elsevier Science B.V. All rights reserved.