The effect of manganese on the dispersion, reduction behavior and active states: of surfaces of gamma -Al2O3 supported copper catalysts was investigated by X-ray powder diffraction (XRD), temperature-programmed reduction (TPR) and XPS technologies. The relationship between the area of metallic copper and the activity of dimethyl ether (DME) synthesis from CO/H-2 was also investigated. The catalytic activity over Cu-MnOx/gamma -Al2O3 catalyst for CO hydrogenation is higher than that of Cu/gamma -Al2O3. The adding of manganese increases the dispersion of the supported copper oxide. For the CuO/gamma -Al2O3 catalyst, there are two reducible copper oxide species; alpha- and beta -peaks are attributed to the reduction of highly dispersed copper oxide species and bulk CuO species, respectively. For the CuO-MnOx/gamma -Al2O3 catalyst, four reduction peaks are observed. The alpha -peak is attributed to the reduction of high dispersed copper oxide species; beta -peak is ascribed to the reduction of bulk CuO; gamma -peak is ascribed to the high-dispersed CuO interacting with Mn; and delta -peak is attributed to the reduction of the manganese oxide interacting with copper oxide. XPS results showed that Cu+ mostly existed on the working surface of the Cu-Mn/gamma -Al2O3 catalysts. Cu promoted the catalytic activity with positive charge, which was formed by means of long path exchange function between Cu-O-Mn. These results indicate that there are synergistic interactions between the copper and manganese oxide, which are responsible for the high activity of CO hydrogenation.