The elastic properties and thermal expansion coefficients of two‐phase ceramic bodies were determined in order to study the effect of the difference in thermal expansions of the two phases. Room‐temperature elasticity was determined by a dynamic method. These values were extrapolated to theoretical density to obtain values for the fully dense bodies. Thermal expansion, measured on a precision dilatometer at 25° to 350°C, was independent of porosity. Experimental values of elastic moduli and expansion coefficients were compared with values given by several theories. Where the difference in expansion coefficients was small the experimental and theoretical values of elastic moduli and expansion coefficients were in agreement. Microscopic examination of these bodies did not reveal any internal cracking. When the difference in expansion coefficients became large enough, the experimental data were scattered and not in agreement with theory for either the elastic properties or expansion coefficients. Microscopic observations of these specimens revealed microc