Densification behavior of the lamellar walls in freeze-casted Al₂O₃ has been investigated in terms of the densification kinetics. To describe the densification kinetics, the thick lamellar walls was considered as bulk thus Coble’s densification theory was adopted. As sintering temperature increased, the bulk theory revealed predominant densification mechanisms as grain boundary diffusion below 1500 ^oC whereas lattice diffusion above 1500 ^oC. This type of shift in densification mechanism is quite general, however, significantly lower activation energy was measured for grain boundary diffusion as 72.17 kJ/mol below 1500 ^oC. In contrast, a similar value to the general case for lattice diffusion, 455.83 kJ/mol was measured above 1500 ^oC. The drop in the activation energy at the lower temperature range can be attributed to Na-containing glassy phase at grain boundaries. This can cause rapid atomic diffusion and easy grain rearrangement and therefore rapid densification during initial stage of sintering. That effect would be significant where grain boundary diffusion dominates below 1500 ^oC but meager if lattice diffusion dominates above 1500 ^oC. Meanwhile, grain boundaries without the glassy phase reveal numerous oxygen vacancies, possibly due to the incorporation of divalent impurity, Mg. An investigation of the dry boundary itself suggests that the addition of a divalent element can be a beneficial way to improve the grain boundary diffusion. The overall densification kinetics appears to be governed by concurrent mechanism occurred at the wet boundary and dry boundary. Both resulted from the segregation of intrinsic impurities, emphasizing the need for the proper selection of dopants to determine the grain boundary characteristics and hence potential densification strategies based on sintering science.