The long-term performance of the bifunctional catalyst composed of MgO-modified HZSM-5 and Cu/ZnO/Al2O3 for steam reforming of dimethyl ether (SRD) is studied under the same conditions. Although the surface chemical state and acid property of 1.55-2.47 wt% MgO modified H-ZSM-5 are almost the same, a significant impact of MgO contents on the stability of the bifunctional catalyst is observed from the 50 h SRD results. The initial dimethyl ether conversion (around 100%) and H-2 yield (similar to 95%) over the optimal bifunctional catalyst with 2.17 wt% MgO modified H-ZSM-5 is still kept over 90% at 50 h. Combining the characterization data of spent catalysts and SRD results, the synergetic effect between the MgO-modified H-ZSM-5 and Cu/ZnO/Al2O3 is rigorously revealed as the key factor in determining the stability of the bifunctional catalyst for SRD. These results demonstrate that MgO-modified H-ZSM-5 is a promising and efficient solid acid for SRD. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.