Methane steam reforming (MSR) over a Rh-loaded Ce0.15Zr0.85O2 catalyst in a membrane reactor was investigated. An yttria-stabilized zirconia (YSZ) membrane used in the membrane reactor showed an ideal H-2/N-2 selectivity of 6.6 at a H-2 permeance of 3.3 x 10(-6) mol m(-2) s(-1) Pa-1 at 500 degrees C. Methane conversions in the membrane reactor were higher than those in a packed bed reactor due to the sufficient permeation rate of hydrogen, which shifted the equilibrium, reaching 82% at 550 degrees C. To evaluate the stability of a membrane reactor, the methane conversion was measured as a function of time. As a result, no significant change in methane conversion was evident at 500 degrees C for 7 h.