Abstract: A two-parameter model (TPM) for determining the effective diffusivities (De) in porous solids has been proposed. The model is applicable to monodis-perse and/or bidisperse pore systems. The resultant expression ot the model for De may be written as: where w and are adjustable model parameters, evaluated from steady or unsteady state diffusion measurements and independent of pore-size distribution and other textural data. Applying TPM to the results of steady and unsteady state diffusion measurements in literature and this article, it is found that the parameters are independent of measurement conditions such as carrier gas, tracer, temperature and pressure. It is concluded that TPM serves well as a reflection ot the textural characteristics of porous solids.