Modified MFI-type zeolite membranes were investigated as high-temperature water-gas shift (WGS) membrane reactors (MRs) in combination with a nanocrystalline Fe/Ce WGS catalyst. The effects of the MR operating conditions and the membrane separation performance on the CO conversion (χCO) were studied experimentally and by calculations using a simple one-dimensional plug-flow reactor (PFR) model. The experimental results showed that, at high temperatures (e.g., >500 °C), the zeolite MR with moderate H2 selectivity (e.g., αH2/CO2 ∼ 31, and αH2/CO ∼ 25) and permeance (Pm,H2 ∼ 0.9 × 10–7 mol s–1 m–2 Pa–1) was capable of overcoming the limit of equilibrium CO conversion and χCO of the MR could be further enhanced by increasing the reaction pressure while keeping the permeate pressure unchanged. At high temperatures and high reaction pressures, CO is rapidly consumed by a fast reaction that minimizes the membrane permeation of unreacted CO; meanwhile, the efficiency of H2 removal is improved as a result of the i...