Adamantylammonium (ADNH(3)(+)) was complexed with [18]crown-6, forming a supramolecular cation of (ADNH(3)(+))([18]crown6), which was introduced into a [Ni(dmit)(2)](-) salt as a supramolecular rotor. The cation layers were alternately arranged with [Ni(dmit)(2)](-) layers in the crystal, in which the molecular rotation of (ADNH(3)(+))([18]crown-6) was confirmed from the temperature-dependent solid-state H-1 NMR.