Utilization of the mathematical model of gas permeation through a ceramic membrane consisting of a support and one separation layer is presented. The influence of errors in measured variables upon reliability of determination of structure parameters of the separation layer is discussed. The usability of the permeation method for the pore size determination was verified by fitting computer generated pseudoexperimental data with Gaussian distribution and preselected variance. All calculations were performed for hydrogen but results for other gases will be similar.