Abstract: The reduction characteristics of nickel catalysts have been investigated by thermoconductivity-temperature-programmed-reduction (TC-TPR) technique. Results showed that on these catalysts there exist three species of nickel oxide, for which the reduction temperatures were 400-500, 600-650, >750℃ and activation energies were 16.1,28,5, 65.5 kcal/mole, respectively. Their relative contents were markedly affected by preparation method, pretreatment conditions and reoxidation temperatures of the catalysts. Therefore, these species of nickel oxide are mutually convertible according to operating conditions.