The adsorption separation of the isomeric dimethylnaphthalene (DMN) mixture of 2,6- and 2,7-DMN in supercritical carbon dioxide was performed. The experiment was carried out by using various zeolites as the adsorbent at the temperature 308.2 K and the pressures 12.0, 14.8, and 19.8 MPa. It was found that a suitable zeolite exists for the separation of the DMN mixture and that the zeolite can adsorb 2,7-DMN selectively. It shows the possibility for the adsorption separation of the DMN mixture in supercritical carbon dioxide.