To easily and safely obtain in high yield and purity the subject compound useful as e.g. an intermediate for medicines, agrochemicals, dyes, etc., by dealkylating an alkoxynaphthaldehyde in the presence of aluminum iodide.

This compound, a hydroxynaphthaldehyde of formula II, is obtained by dealkylating (A) a compound of formula I (R is an alkyl, pref. 1-6C alkyl) in the presence of (B) aluminum iodide (using 2-5(esp. 2.5-3.5) equivalents of the component B based on the component A e.g. at 0-45 (esp. 20-40)°C). The dealkylation can be performed in a solvent such as benzene, toluene or xylene, and the component B may be a reagent on the market, or can be prepared by reaction between aluminum powder and iodine.