A numerical procedure was developed for simulating moisture migration in multi-component breakfast cereal systems. The transport of moisture within cereals and raisins was described by equations of unsteady state diffusion. The surface moisture concentration of raisins and cereals was assumed to be in equilibrium with the package void-space moisture concentration and was obtained from the corresponding GAB moisture isotherm equations. Using diffusion coefficients determined from regression analysis of the series solution for gain or loss of moisture, the simulation accurately predicted the moisture gain by cereal at 25°C and 75% relative humidity and loss from raisins when stored alone at 25°C and 11% relative humidity. Simulated curves were obtained using an explicit finite difference scheme to model unsteady state moisture diffusion within raisins and cereals when stored in an impermeable package at 25°C. These simulations allowed visualization of the effect of increasing or decreasing the moisture diffusion coefficient in raisins on the moisture migration pattern within the system.