The large spherical pores were generated by foaming process, and the small cellular pores on internal walls were derived from the organic matter removal and mullite particle accumulation. As sintering temperature increased from 1350 ฐC to 1500 ฐC, the amount of small cellular pores on the internal walls decreased, which was caused by sintering densification. Thus linear shrinkage and bulk density increased with increasing of sintering temperature. But when sintering temperature achieved 1550 ฐC, the amount of small cellular pores on the internal walls increased, which might be caused by localized nonuniform grain growth and shrinkage at high temperature. Typical mullite grain nonuniform