A new technique has been developed for preparing high porousity ceramics. Spray freeze drying of magnesium sulfate aqueous solution produced porous fine salt particles, which were calcined to porous particles of magnesium oxide. The oxide particles were treated to form magnesia ceramics that showed high porosity in a range of 0.5 similar to 0.85. The following equation which can assess ceramics strength for high porosity is proposed. sigma = sigma(o)(1 - a epsilon)(m) where sigma[Nm(-2)] strength, epsilon[-] porosity and sigma(o), a, m constants. The validity of the equation is confirmed by the present investigation data and also the ones published.