Based on earlier studies and the authors' original idea, the IH method was proposed as a means of estimating mutual diffusion coefficients as a function of moisture content and temperature. The diffusion coefficient was determined from the coating temperature history during coating drying experiments with constant-temperature hot air. A senes of computer simulations was performed for an imaginary Fick-type coating of polyvinyl alcohol-water and the coating temperature history during drying was obtained. The diffusion coefficients estimated by the IH method showed good agreement with the cited diffusion coefficients used in the drying simulations, suggesting the validity of the IH method.