A series of Cu/Al2O3 catalysts with different contents of samarium were prepared by the incipient wetness method and used in hydrogen production by methanol steam reforming. The role of samarium addition and the effects of the samarium loading on the surface structure and catalytic properties were investigated. The H-2-TPR results indicated that the doping of samarium led the active Cu particles more difficult to be reduced. The XRD, XPS and HAADF/STEM data suggested that the presence of samarium favored the formation of larger Cu particles. The highest hydrogen yield was obtained over Cu/Al2O3 catalyst without samarium in the temperature range 200-300 degrees C. Moreover, the presence of samarium also resulted in the decrease of methanol conversion. These phenomena are due to the fact that the presence of samarium could inhibit the reducibility and lead to clustering of the active Cu particles, thus, reducing the activity of the catalysts.