Abstract: The present invention provides a method for producing .beta.-methylnaphthalene from an inexpensive and easily available feed oil. According to the invention, highly pure .beta.-methylnaphthalene adequate for industrial use can be mass-produced at reduced costs. The method comprises catalytic hydrodealkylation of a feed oil containing an alkyl naphthalene having at least two methyl groups in the presence of a catalyst having at least one metal species of selected from the group consisting of vanadium (V), chromium (Cr), nickel (Ni), rhodium (Rh), platinum (Pt), iridium (Ir), and compounds of these metals as an active component and a carrier therefor containing at least one of alumina and silica as its primary component, with a hydrogen partial pressure of 1 to 50 kgf/cm.sup.2, at a temperature of 450.degree. C. to 650.degree. C., and for a contact time of 3 to 35 seconds. The method of the invention is excellent in that it affords .beta.-methylnaphthalene of a chemical grade with a high yield.