The sintering behaviors of the glass-alumina composites for low firing temperature were investigated as functiions of the volume fraction of alumina powder and the particle size with respect to porosity and pore shape. As the volume fraction of alumina powder was increased or the particle size of it was decreased, the sintering temperature of open pore-closing was raised. When the volume fractions of alumina which had 2.19$mu extrm{m}$ median diameter were increased with 20, 30, 40, and 50%, the sintering temperatures of open pore-closing were 425, 450, 475, and 500$^{circ}C$. And when the median particle size of alumina was diminished from 2.19$mu extrm{m}$ to 0.38$mu extrm{m}$, the sintering temperature of open pore-closing was increased from 450$^{circ}C$ to 475$^{circ}C$. Especially, the sintering temperature, which showed maximum density, was corresponded with the stage of open pore-closing and after achieving maximum density over heating resulted in dedensification of specimen, so called, over-firing behavior.