A kinetic model based on the postulates of Langmuir-Hinshelwood has been proposed for the catalyst deactivation by coke in heterogeneous polymerizations. The originality of the model lies in the fact that deactivation is also taken into account during the initiation period by defining the activity as the useful fraction of active sites throughout the polymerization. The validity of the proposed deactivation kinetic model has been shown for the polymerization of gaseous benzyl alcohol in an ample range of operating conditions : catalysts (silica/aluminas and a HY zeolite) with different acidity and different porous structure, temperature, and monomer concentration. The results are compared with those of the previously defined model, where activity referred to the maximum polymerization rate.