A series of alumina supported Ni, Mo and Ni-Mo catalysts prepared by impregnation or coimpregnation were tested to investigate the effects of Ni-Mo interaction on their structural properties and activity/selectivity characteristics in CO hydrogenation. The Ni and Mo contents of the catalysts were varied between 0-15 wt% according to a factorial experimental design. The results of CO hydrogenation tests reveal that the specific activity of the active sites changes with Mo loading, Ni:Mo molar ratio and total metal loading. Introducing Mo as the second metal increases the total hydrocarbon production as well as the C-2-C-4 hydrocarbons selectivity in the 498-573 K temperature range. Lower H-2/CO molar ratios increase C-2-C-4 selectivity, and this effect is enhanced with Mo addition especially to samples with higher Ni loading.