A derivative of the Si3N4 ceramic is the quaternary SiAlON solid solution. In this paper the characteristic stress-strain response of the,Band c-SiAION phases is investigated using an ab initio computational procedure, for the gamma(11) strain component, where different substitutions of the atomic pairs, Al-O, were performed. From the modeled data the 'ideal' strengths and other material constants were estimated for the two polymorphs. Estimates of the elastic constants were found to be in reasonable agreement with existing data.