Porous ceramics were manufactured using the foaming method for the development of inorganic insulating materials. Silica fume and SiO2 were used as main raw materials, and bentonite was used as a rapid setting agent for uniform structure formation of porous ceramics. The porous ceramics were sintered at 1200°C, and porosity, density, compressive strength, microstructure and thermal conductivity were analyzed. As the content of silica fume to SiO2 of the porous ceramics increased 70 to 90 %, the specific gravity increased from 0.63 to 0.69, and the compressive strength increased from 9.41 Mpa to 12.86 Mpa. But, the porosity showed a tendency to decrease from 72.07 % to 70.82 %, contrary to the specific gravity. As a result of measuring the thermal conductivity, the porous ceramic with a silica fume content of 70 % showed a thermal conductivity o f 0.75 to 0 .72W/m∙K at 25 t o 800°C, respectively, and, another that a silica fume content of 90 % showed a 0.66~0.86W/m∙K. So the l ower t he s ilica f ume content, t he l ower t he t hermal c onductivity, which w as c onfirmed to b econsistent with porosity result. As a result of microstructure analysis using SEM (Scanning Electron Microscope), pores in the range of tens to hundreds µm were observed inside and outside the porous ceramic, and it was confirmed that the pore distribution was relatively uniform.