Recently, diffusion theory has been increasingly applied to describe the drying of agricultural grain. This requires a knowledge of the diffusion coefficient as a function of temperature and moisture content. Based on published data, a relationship was developed for the diffusion coefficient of corn. Comparisons with experiments show that the diffusion equation more exactly fits the drying curve than do some well-known, semi-empirical relationships. However, it should be stated that the semi-empirical models can give reasonable results for practice.