A contribution is given to the theoretical research on the stiffness o
f ceramic materials, under the approximation of the average stress fie
ld, the relation E = E-o(1-p)/(1 + 2.5p) is derived to describe the de
pendence of the modulus of elasticity on porosity. The prediction of t
his model is consistent with the experimental data from several cerami
cs such as reacting sintered Si3N4, MgO and MgAl2O3.