The title complex [K (dndb ) (H2O) (NCS ) ], (dndb = trans-dinitro-dibenzo-- 18 -- crown -- 6 -- ether ) crystallied in triclinic system, space group Pl wit h unit celldimensions a= 7. 844 (4), b= 11. 979(8), c= 14. 436(11) A; a= 75. 62(6), β=80. 15(5), γ= 71. 94(5)°, M.= 1131. 39, V= 1243(2) A3, Z= l, F(000) = 588, D.= 1. 511 g/cm3, μ= 10. 5 cm-l (MoKa). The final R= 0. 045 for 2740 observed reflections (I＞3σ). The title complex molecule is a dimer complex and the potassium(I) ionis nine--coordinated, being bonded to one NCS-- anion, one H2O molecule, six oxygenatoms of a crown ether ligand and an oxygen atom of a nitro of another crown ether ligand. The potassium(I) ion and the nine atoms bonded with it are all in two planeswhich are approximately vertical with each other. The trans--dinitro-- dibenzo-- 18 -- crown6 is a heptadentate ligand.