An experimental method has been developed to measure the effective thermal conductivity of a bed consisting of CaCl2 reactive particles accompanying the variations of thermophysical properties with the progress of gas-solid reactions. Using this method, measurements have been performed for the beds in CaCl2/CH3NH2, CaCl2/CH3OH and CaCl2/NH3 reaction systems. The effective thermal conductivity of the reactive bed, which was reduced to less than one half of that of the initial anhydrous CaCl2 bed, increased with the absorption and decreased with the desorption of the reactive gas. Corresponding to the variations of effective thermal conductivity, the void fraction varied during the reaction cycles, The relation between the effective thermal conductivity and the void fraction inside the particle indicates that the main cause of the reduction in the effective thermal conductivity is attributed to a decrease in the thermal conductivity of the solid product.