Modeling of non-catalytic gas-solid reactions (NCGSRs) carried out using the cellular automata (CA). A computerized program based on the CA rules was developed in MATLAB. A porous medium with known porosity was constructed in two-dimensional at first using the Boolean variable and the CA rules. The process of gas diffusion and reaction through the porous medium was then simulated using the CA rules. The simulation results have been compared to experimental data of reduction of chromium oxide with methane (Khoshandam et al., 2006) [10] and a mathematical model based on the grain model. The simulation results using CA show better agreement with experimental data than the grain model results. © 2012 Elsevier B.V.