A novel two-dimensional 18-crown-6 (18-C-6) complex, [Na-2(18-C-6)(2)(H2O)(3)][Ni(dmit)(2)](2)(.)(18-C-6) (dmit, 4,5-dimereapto-1,3-dithiole-2-thione, C3S52-) (1) has been synthesized and characterized by elemental analysis, IR spectrum and X-ray diffraction analysis. I belongs to triclinic, space group P-1 with cell dimensions, a = 13.227(10), b = 12.8421(11), c = 13.8671(12) Angstrom, alpha = 83.715(2), beta = 88.477(2), gamma = 71.850(2)degrees, V = 1904.5(3) Angstrom (3) Z = 2, D-calcd = 1.566 g/cm(3), F(000) = 932, R-1 = 0.0415, wR(2) = 0.0805. It consists of one [Na-2(18-C-6)(2)(H2O)(3)](2+) complex cation, two [Ni(dmit)(2)](-) complex anions and Due free 18-C-6 molecule. The complex shows two-dimensional structure assembled by (SS)-S-... and (NiS)-S-... weak interactions.