The surface and morphological properties of molybdenum trioxide were characterized using microcalorimetric and SEM methods. The number of acidic and basic sites were measured by NH3 and SO2 adsorption, respectively. According to the microcalorimetric data, strong dissociative adsorption of NH3 takes place on the surface, while there is no interaction between the MO(3) lattice and SO2 gas. The chlorination kinetics of MO(3) with gaseous CCl4 were studied by thermogravimetry. The values of the apparent activation energy and the formal reaction order were calculated from the temperature and partial pressure dependence of the initial rate, respectively. From the results obtained, the combined control of pore diffusion and chemical reaction, as well as the dissociative adsorption of CCl4, were deduced. Due to the very low porosity of the solid particles, in addition to the reaction occurring in a zone near the pore tunnels, chlorination at the external surface cannot be neglected. Thus, to describe the conversion versus time curves, a kinetic model was proposed based on the different linear rates of the interfacial chemical reaction at the external surface of the particles and that in the reaction zone controlled by pore-diffusion processes. Using this model, a fairly good correspondence between the measured and calculated kinetic curves was obtained.