A method for concentrating 2,6-dimethylnaphthalene in a dimethylnaphthalene isomer mixture includes supplying the dimethylnaphthalene isomer mixture to an adsorption column packed with Y-type zeolite. In this instance, by setting the value derived from the expression (u1/3/&egr;)d−5/3 at 14 (m5/3 s−1/3 kg−1) or more, the concentration ratio of 2,6-dimethylnaphthalene to 2,7-dimethylnaphthalene can be 2.0 or more. u here represents the linear velocity (m/s) of the dimethylnaphthalene isomer mixture supplied to an adsorption column, &egr; represents the packing density (kg/m3) of Y-type zeolite, and d represents the grain size (m) of the Y-type zeolite.