(1) The evaluation of the activation energy of nonisothermal sintering based on the Arrhenius plot of ln(ε˙T) versus the reciprocal of the absolute temperature can be influenced by the heating rate due to the difference of the relative contribution of Dl and Db to the densification rate. Therefore, nonisothermal sintering is not a proper process to evaluate the activation energy of sintering. (2) Pore morphology also plays a role in evaluating the activation energy of sintering. (3) The apparent diffusion coefficient in sintering finegrained and high-purity alumina is determined by the aluminum ion via grain boundary.