Hydrated sodium silicate was synthesized by hydrothermal reaction using anhydrous sodium silicate. The optimum additions of water was 25wt% to make hydrated sodium silicate with homogeneous and purposed water contents. Porous ceramics with homogeneous microstructure and spherical closed pore can be fabricated by elimination of the large pores(a few mm in size) which was formed during first heat treatment through the decomposition of water. Spherical closed pore was formed above $600^{circ}C$ and the pore size was increased with increasing second heat treatment temperature due to growth of pores. The size of spherical closed pore was varied from 35 to $233;{mu}m$ and specific gravity was varied from 0.2 to 1.02 depending on the combinations of the first and second heat treatment temperature.