Steam reforming of methanol over a Cu/ZnO/Al2O3 catalyst has been investigated over the temperature range of 493–573 K at atmospheric pressure in a fixed bed reactor. A series of catalysts were prepared by wet impregnation and characterized by atomic absorption spectroscopy, surface area, pore volume, pore size and X-ray diffraction technique. The X-ray photoelectron spectroscopy and thermogravimetry analysis of deactivated catalyst was done to investigate the nature of coke deposited on catalyst surface. The rate of coke formation and its influence over catalyst deactivation have also been studied. A monolayer–multilayer mechanism is proposed to model the coke formation with time and to study its effect on methanol conversion. Deactivation model was coupled with the kinetic model available in the literature to study the effect of coke formation on activity. The parameters of deactivation model for the Cu/ZnO/Al2O3 (10/5/85 wt.%) catalyst have been determined by fitting the experimental data for methanol conversion and coke deposition. This model achieved the key objective of predicting the experimental observation with 95% accuracy.