The partial oxidation of methane (PORI) reaction is conducted using several nickel catalysts which show high activities in carbon dioxide reforming of methane. Temperature programmed reaction and thermogravimetric analysis show that a reduced state of nickel is required to start the POM reaction, and that carbonaceous deposition occurs on alumina with high nickel contents. The temperature profile of the catalyst bed during the POM reaction suggests that this reaction consists of two consecutive reactions; methane combustion, following by reforming reactions (with steam and carbon dioxide), The heat caused from methane combustion keeps the temperature high enough to progress the reforming reactions. To suppress the carbonaceous deposition which causes catalytic deactivation and plugging of the reactor, carbon deposition-removal (D-R) treatment is applied in the POM reaction, On the basis of the hypothesis that active co res forming carbon whiskers are different from surface active sites for the main reaction, this treatment has been proposed to only remove or deactivate the former core nickel. It was concluded that this treatment makes the catalyst inactive for carbonaceous deposition with only a small influence on the main reaction activity.