Active charcoal has been discovered to have catalytic activities for dehydrogenation of hydrocarbons such as n-paraffins, isoparaffins, cycloparaffins and olefins at temperatures ranging from 400 to 500°C. Rates of reaction when using active charcoal as catalyst were larger than those of reaction using silica-alumina catalyst. The catalyst activity decreased in earlier stages of reaction, but after three hours the catalyst activity and its selectivity remained essentially unchanged with the elapse of time. Aromatic hydrocarbons were obtained at a fairly high yield when feed hydrocarbons had more than six carbon atoms within its main skeleton. The reactivities of hydrocarbons with the same carbon number were high in the following order: olefin>cycloparaffin>paraffin. The reactivities of feed hydrocarbons increased with the increase in its carbon number but higher selectivity were obtained when lower hydrocarbons were reacted. For example, isopentens were formed from isopentane at 460°C with the selectivity of about 90 mole percent. No skeletal isomerization of reactants or products did not occur. The active charcoal in this study is thought to be a kind of solid radical catalyst and accelerates the radical reaction of hydrocarbons.