Abstract The crystal structure of anhydrous copper 8-hydroxyquinolinate has been determined by the two-dimensional Fourier method. It is monoclinic and has been shown to belong to the B21/a space group, with eight molecules in a cell of the dimensions: a=23.66, b=8.72, c=15.30Å and β=117.5. A copper atom is surrounded by four atoms with Cu–N distances of 1.92 and 1.90Å, and Cu–O distances of 2.01 and 2.07Å. Two nitrogen and two oxygen atoms form a square and are coplanar with the copper atom. The closest approach of adjacent chelate molecules occurs along the b axis and in the [101] direction, where the interplanar distances are 3.36, 3.47, and 3.32Å. These chelate molecules are grouped in pairs around the symmetry center at the point of origin with a Cu–Cu bond of 3.45Å. The perpendicular distances between successive dimeric molecules given above are almost the same within the range of experimental error. A π-bond overlapping of molecules is considered to be a part of the binding forces between such layers. The metal-metal bond is presumably the same as that in nickel dimethylglyoxime.