The solid-liquid wetting factor, f, for solid dissolution in a liquid with and without chemical reaction was experimentally determined in a fixed bed three-phase reactor with downward concurrent gas and liquid flows (Trickle Bed Reactor). The method employed consisted of comparing the volumetric solid-liquid mass transfer coefficient obtained when two phases (liquid and gas) circulated through the bed, with those coefficients obtained at liquid full bed conditions, maintaining the intrinsic liquid velocity constant. The chemical system selected was benzoic acid and acetylsalicylic acid as solid phases, water and sodium hydroxide in aqueous solution, and atmospheric air. Experiments were carried out in which the flow of both phases was modified, obtaining a direct dependency of f with the flow and holdup of liquid. The gas flow effect over f was not important in the flow regime studied, defined as the low interaction regime. Furthermore, the wetting factor is not affected by the nature of the solute and by the presence of a chemical reaction.