The microstructure evolution and densification kinetics of alumina containing 10 and 20 vol% calcium aluminosilicate glass were studied, for sintering under vacuum and air at 1600 degrees C. Residual porosity was always present in the air-fired samples. The kinetic analysis lent strong support to the notion that trapped gases inhibited the densification and limited the attainment of full density. The samples containing 20 vol% glass were able to reach full density during vacuum sintering. However, the samples containing 10 vol% glass contained some residual porosity even after vacuum sintering, which was attributed to the preferential volatalization of liquid phase.