Abstract A new Monte Carlo simulation of CO oxidation over a non-isothermal supported catalyst is presented. It uses the Monte Carlo method applied to multiple 2D crystallites distributed on a flat support in combination with the partial differential energy balance to simulate the non-isothermal reaction on supported catalysts. The simulation predicts ignition and extinction transitions similar to those observed during a temperature programmed reaction experiment. However, no auto-oscillatory behavior is predicted when the surface is assumed to have constant activity. Stochastic fluctuations at each crystallite cannot be synchronized through the thermal coupling to form global oscillations. The model was extended to include a surface with variable activity. In this case an oxidation/reduction mechanism altering the oxygen sticking coefficient provides a bistable mechanism for auto-oscillations. This variable activity model predicts auto-oscillations and changes in oscillatory behavior with temperature and O 2 /CO ratio similar to those experimentally observed. Simulation results also show that thermal communications among crystallites affect the shape of global oscillations. Irregular and chaotic oscillations are predicted when there are differences in the crystallite size, activity, and distribution of the crystallites on the support.