Pore size has been found to strongly depend on the sintering program in the preparation of porous ceramic membranes. In this paper, a model was developed to predict the variation in pore size and porosity of membranes during the sintering process. A comparison of shrinkage characteristics was made between the sintering processes of supported membranes and unsupported membranes. For supported membranes, the effect of restriction coming from a rigid substrate on the sintering behavior has been taken into account in the calculation. It is predicted that the pore size increases in supported membranes and decreases in unsupported membranes as the sintering temperature is increased. Calculations also showed that the loss of porosity in the supported membranes was less than that in the unsupported membranes. In order to verify reliability of this model, unsupported and supported membranes were prepared with alpha-Al2O3 powders at the sintering temperatures ranging from 1125 A degrees C to 1325 A degrees C. The pore size and porosity were measured by gas permeation technique and Archimedes's method. The experimental results for the unsupported and supported alpha-Al2O3 membranes showed a good agreement with those calculated from the model. Therefore, this model provides an effective tool in predicting the porosity and the pore size of ceramic membranes at the different sintering temperatures.