Using mathematical model and experimental method, the thermal and non-catalytic decomposition of hydrogen sulfide in membrane reactor with porous membrane of Knudsen diffusion characteristics was investigated. It was found that in terms of the yield, the membrane reactor can have its merit over the reactor without membrane in the case where inverse of space velocity 1/S-v is larger than some critical value, and there is a maximum value of specific yield SY defined as the ratio of yield for the membrane reactor to that for the reactor without membrane, SYmax when almost all the reactant permeates through the membrane. Lower a product of permeance PH2 and the ratio of membrane area to reactor volume 1/h, P-H2/h and higher pressure in the main chamber p(R) is favorable to obtain higher SYmax and the average concentration of H-2 in the permeate. But the reactor length needed to permeate almost all the reactant increases. There might exist optimum PH2/h from the viewpoint of cost. Using membrane reactor integrated with ZrO2-SiO2 composite membrane, the reaction was carried out under the following conditions: T = 973 and 1023 K, p(R) = 0.11 and 0.20 MPa, pressure in the permeate chamber of 5 kPa and 1/S-v = 21-77 s. With the experimental condition, T = 1023 K, p(R) = 0.11 MPa and 1/S-v = 77 s, SY was 0.35 in maximum. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.