The reduction of cobalt catalysts supported on Al2O3, SiO2, and TiO2 was investigated using a closed system filled with hydrogen gas. Effects of support and metal loading on the rate of reduction were also discussed. The activation energy of reduction increased in the following order : Co/TiO2 < Co/Al2O3 < Co/SiO2. For different metal loadings, it was found that the catalyst with the higher loading was more readily reducible than that with the lower metal loading. This was confirmed using the results from measurements of particle size, amount of CO adsorbed and activity.