Alumina has been pretreated in the presence of medium and then used to prepare the supported Co catalysts. These modified supports and the respective catalysts have been thoroughly characterized by means of methods such as BET, pore size distribution, X-ray diffraction (XRD), ammonia temperature-programmed desorption (NH3-TPD), pyridine infrared spectroscopy (Py-FTIR), KBr-IR spectroscopy (FTIR), temperature-programmed reduction (TPR), oxygen titration, hydrogen chemisorption, in situ diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) and CO hydrogenation to understand how chemically-treated alumina influences the properties of Co catalysts. These characterizations clearly show the changes of morphology (surface area, pore volume, pore size distribution and crystallite phase) as well as chemical properties (e.g. acidity) of the supports. Although the cobalt oxide crystallite sizes of the oxidic catalyst precursor are almost unaffected by different support pre-treatment, the reducibility of these catalysts vary greatly. And the support pre-treatment remarkably influences the adsorption and catalytic properties of these Co catalysts. The acetic acid-treated support has a negative effect on the catalytic properties of Co catalyst, whereas the ammonia and ammonium nitrate-treated samples show pronounced effects on the catalytic behaviors of Co catalysts.