A kinetic model is proposed for deactivation by coke of a HZSM-5 zeolite catalyst used in the transformation of methanol into hydrocarbons in the 573 - 723 K range. The attenuating effect on coke deposition due to the presence of water in the reaction medium was quantified by a parameter that increases with reaction temperature. The slower deactivaton of the methanol dehydration step compared to the formation steps of olefin and gasoline lumps is taken into account. In view of the results, water content in the reaction medium is an efficient variable for controlling the results of activity-selectivity-deactivation. This model is not applicable for a temperature of 723 K when water content in the reaction medium is high, due to the fact that under these conditions the zeolite is subjected to irreversible deactivation.