Studies of the adsorption mechanism were carried out experimentally and numerically were based on the temperature data inside the adsorbent particle and adsorptivity profiles at the adsorption/desorption process by a volumetric method using two different types of relatively large silica-gel particles. Although the adsorption equilibria of the two silica-gels showed different types of curve, the intraparticle temperature profiles show almost the same, i.e. the temperature at the surface is initially slightly higher than that at the center, and then all points reached their respective maximum temperatures at the same time, with the temperature at the center point being the highest and at the surface the lowest. These tendencies were fitted with the simulation results of the molecular diffusion model rather than those of the surface diffusion model. This shows that the adsorption phenomena can take place not only at the surface but inside the adsorbent particle, implying that molecular vapor diffusion has a great influence on adsorptivity, therefore, it can be said that the molecular diffusion model was adopted to describe silica-gel/water adsorption.