In the title compound, C24H24N2O2, the five-membered ring of the indoline ring system adopts an envelope conformation with the spiro C atom at the flap. The dihedral angle between the benzene ring of the indoline ring system and the naphthalene ring system is 71.70 (7)°. In the crystal structure, pair of weak C—H...O hydrogen bonds link the molecules into centrosymmetric dimers.