A simple permporometry method based on varying membrane temperature is demonstrated for measuring the pore size distribution of active layer in asymmetric ceramic membranes, This modified permporometry technique can be used to characterize asymmetric ceramic membranes with pores of 2 to 100 nm in diameter. The pore size distribution data of the gamma-Al2O3 membranes measured by the modified permporometry using cyclohexane and carbon tetrachloride as condensable vapor agree favorably with those measured by the nitrogen adsorption porosimetry and permporometry data reported in the literature.