The effect of water on cobalt speciation in the synthesis of Co2+/ZSM5 catalysts is quantitatively studied by the combined use of macroscopic and local characterization techniques, TPR and X-ray absorption spectroscopies, respectively. The addition of a small quantity of water to cobalt acetate and zeolite during the preparation of Co2+/ZSM5 by solid-state reaction favors cobalt dispersion and migration into the zeolite. It also inhibits the formation of extraframework phases (Co3O4 particles, cobalt phyllosilicate). Dissociation of solid cobalt acetate upon contact with water is thought to be the driving force for enhanced cobalt migration into the zeolite.