A rational technical process for producing dialkylnaphthalenes from
petroleum-derived starting materials which exist in abundance is established. The process for producing dialkylnaphthalenes contains the steps (1), (2), (3), and (4): (1) 1st step which is for catalytically hydrodealkylating a stock oil containing a substantial amount of
naphthalene and / or alkylnapthalenes, separating a product oil form a
product gas, and separating and recovering a fraction composed mainly of
naphthalene and / or methylnaphthalene from the product oil; (2) 2nd step which is for catalytically alkylating or catalytically transalkylating the fraction, recovered in the 1st step, composed mainly of
naphthalene and / or methylnaphthalene directly without pretreatment for purification, with an alkylating agent or transalkylating agent to prepare alkylnaphthalenes; (3) 3rd step which is for separating and recovering dialkylnaphthalenes from the alkylnaphthalenes obtained in the 2nd step; and (4) 4th step which is for returning at least a part of the residual fraction, after the separation and
recovery of dialkylnaphthalenes in the 3rd step, as at least a part of the stock oil in the 1st step and / or at least part of the alkylating agent or transalkylating agent in the 2nd step to the corresponding step.