The salt diffusion in fully saturated brick at isothermal condition is investigated. A commonly used experiment methodology, diffusion cell method, is adopted to estimate the salt diffusion coefficient. The mathematical model is developed. An approximate analytical solution is given. The solution agrees with the numerical solution. The analytical solution has applications in a wide number of fields with diffusion cell method. Furthermore, the diffusion coefficients of different types of salt for different types of brick are discussed. (c) 2005 Springer Science + Business Media, Inc.