In the title compound, K[Ni(C3S5)(2)]C20H24O6 .C3H6O, K+ is incorporated in the cavity of the 1,4,7,10,13,16-hexaoxa-2,3:11,12-dibenzocyclooctadeca-2,11-diene (DB18c6) molecule and is coordinated by the six DB18c6 O atoms and the propanone O atom. Two {K+ (DB18c6)[(CH3)(2) CO]} units form a dimer which is aligned in a one-dimensional manner along the a axis through a face-to-face interaction between the benzene rings of neighboring DB18c6 molecules. [Ni(dmit)(2)](-) anions are also aligned along the a axis through side-by-side S . . .S interactions.