Reaction of 8-formylquinoline thiosemicarbazone (HQATSC) with a variety of copper salts yield a series of copper(II) complexes of the type Cu(HQATSC)X2 ·nH2O where X= ½SO4, Cl, NO3 [1]. At minimum one of the anions is involved in the formation of the coordination polyhedron of the complexes. Perchlorate is known as very weak coordinating anion. In order to obtain complexes without coordinated anion, the interaction of HQATSC with copper(II) perchlorate has been undertaken. The complex of the composition Cu(HQATSC)(ClO4)2·2H2O was prepared by mixing acidified ethanol solutions of copper(II) perchlorate and HQATSC in a molar ratio 1:1. On the cooling of the resulting solution, dark green crystals have been obtained, which were filtered, washed with acidified alcohol, followed by diethyl ether, and dried at room temperature. X-Ray investigation showed that the compound crystallizes in thr triclinic space group P1. The structure of the compound Cu(HQATSC)(ClO4)2·2H2O is ionic and is formed by the coordination polymeric cation [Cu(HQATSC)(H2O)(ClO4)]n 2n+ (1D chain), one perchlorate anion in extern sphere and a water solvate molecule. The neutral thiosemicarbazone ligand is coordinated to the copper atom through N, N, S donor set and metal adopts a square planar configuration were the forth position is occupied by water molecule. One of the perchlorate anion is situated in the apical position and the geometry of the complex cation [Cu(HQATSC)(H2O)]2+ seems to be a tetragonal pyramid. The pyramids are assembled in polymeric 1D chain using the coordinated ClO4 - ions, which act as bridges and the real geometry of the Cu(II) cation can be considered octahedral. In the equatorial plane of the coordination core the Cu–N distances are 2.037(4) and 1.964(3) Å, Cu–S is 2.272(1) Å and Cu–O(H2O) is 1.998(3) Å. The axial distances Cu–O(2) and Cu–O(3) (–x–1, –y, –z) are 2.512(1) and 2.520(1) Å.