Cobalt supported alumina catalysts were prepared by slurry impregnation method and calcined the catalysts in different atmosphere. The prepared catalysts were characterized by N-2 physisorption, TPR, XRD, TEM, FT-IR and XPS techniques. The catalyst calcined under hydrogen atmosphere leads to the metallic cobalt of HCP structure and shows the good catalytic activity for Fischer-Tropsch synthesis under the reaction condition. The catalyst calcined under air atmosphere led to the metallic cobalt of FCC structures and shows lower catalytic activity. It was also found that calcination atmosphere and structure of the catalyst have profound effect on the activity and selectivity for Fischer Tropsch synthesis. (C) 2014 Elsevier B.V. All rights reserved.