The modified statistical theory of sintering was used to evaluate the microstructural parameters, such as the average pore radius, grain size, and total length per unit volume of pore, of undoped and doped alumina compacts during the intermediate stage of sintering. The present results further justify the validity of the modified statistical theory of sintering in characterizing the morphological changes of pore channel network. The evaluated data of the evolution of these morphological parameters provide deep insight of the understanding of the mechanism of the effects of particle size distributions, MgO and ZrO2 on breakup of pore channel network. The possible roles of MgO and ZrO2 in the intermediate stage of sintering have been discussed. (C) 2005 Springer Science + Business Media, Inc.