The liquid phase acylation of 2-methoxynaphthalene (2-MON) with acetic anhydride over various solid acid catalysts was investigated under controlled reaction conditions. Only zeolite beta exhibited good regioselectivities to desired 2-acetyl-6-methoxynaphthalene (2,6-AMON). Characterization studies of zeolite: beta samples indicated that acidity affected catalytic activity but not regioselectivity of 2,6-AMON. The secondary structure of zeolite beta particles was found to be an important factor for the selectivity probably because of its effect on diffusion process of reactants into internal pores. When the mole of acetic anhydride used as acylating agent was increased, the selectivity of desired 2,6-AMON product became worse. 1,2-Dichloroethane and dichloromethane were found to be effective solvents giving good regioselectivities of 2,6-AMON. Protiodeacylation took place not only for 1-acetyl-2-methoxynaphthalene (1:,2-AMON) but also for 2,6-AMON.