Using mathematical model and experimental method, the thermal decomposition of hydrogen sulfide in membrane reactor with porous membrane which has Knudsen diffusion characteristics was investigated. With mathematical model, the effect of characteristics of membrane reactor and operating conditions on H-2 concentration in the permeate chamber, y(H2), which increases at higher reaction temperature, lower pressure and higher ratio of cross-sectional area of the permeate chamber to that of the reactor, was evaluated. The reaction experiments with ZrO2-SiO2 porous membrane were carried out under the following conditions : temperature T, 923-1023 K; pressure in the reactor p(T)(R), 0.11-0.25 MPa absolute; pressure in the permeate chamber p(T)(P), 5 kPa absolute and inlet flow rate of H2S f(H2S)(0), 3.2x10(-5)-1.5x10(-4) mol/s. At p(T)(R)=0.11 MPa and f(H2S)(0)=6.4x10(-5), y(H2) increased from 0.02 at T=923 K to 0.15 at 1023 K. With the experimental condition, p(T)(R)=0.11, T=1023 K and f(H2S)(0)=3.2x10(-5), y(H2) was 0.22. 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.