Non-homogeneous distribution of reactants is common when powders are mixed and the conventional modeling treatments for combustion synthesis thus far have only considered uniform systems. The occurrence of the composition heterogeneity is thought to result in local variations of the thermophysical/chernical parameters of reactants, such as density, heat capacity, and thermal conductivity, thus change combustion temperature, propagation velocity, and propagation pattern of combustion front. This study aims to address the composition heterogeneity effect on stable/unstable combustion synthesis by numerical simulation. The Ni + At stable combustion reaction and Ti + 2B unstable combustion reaction are chosen to illustrate the composition heterogeneity effects. The correlations of composition heterogeneities with propagation velocity, combustion temperature, and propagating mode are established in this study. In addition, the comparisons of the composition heterogeneity effects between the stable and unstable combustion reactions are also carried out in this study. (C) 2004 Elsevier B.V. All rights reserved.