PURPOSE: To obtain the titled substance, in high selectivity, with little production of by-products having high boiling point, by the trans-alkylation reaction of a naphthalene compound with a polyalkylbenzene in the presence of an AlCl3 catalyst in a (cyclo)paraffin solvent at a specific temperature.

CONSTITUTION: The objective substance can be produced by the trans-alkylation reaction of a naphthalene compound (e.g. naphthalene, alkylnaphthalene, etc.) with a polyalkylbenzene in the presence of an AlCl3 catalyst at 0W35°C (prefer ably at normal temperature) to an extent to give a naththalene conversion of ≥40wt% (preferably 40W60%). The amount of the catalyst is 0.05W0.4 mol per 1 mol of the naththalene compound, and the ca talyst may be used in the form of a complex with an aromatic hydrocarbon, nitromet hane, etc. When the naththalene compound is solid and is not sufficiently soluble in the polyalkylbenzene, the reaction is carried out in a solvent.

USE: Raw material for the production of β-naphthol, etc.