The title complex, tetra-aqua-{1-[(1H-benzotriazol-1-yl)meth-yl]-1H-1,2,4-triazole-κN(4)}(sulfato-κO)copper(II) sesquihydrate, [Cu(SO(4))(C(9)H(8)N(6))(H(2)O)(4)]·1.5H(2)O, is composed of one copper atom, one 1-[(2H-benzotriazol-1-yl)meth-yl]-1-H-1,2,4-triazole (bmt) ligand, one sulfate ligand, four coordin-ated water mol-ecules and one and a half uncoordinated water mol-ecules. The Cu(II) atom is six-coordinated by one N atom from a bmt ligand and five O atoms from the monodentate sulfate ligand and four water mol-ecules in a distorted octa-hedral geometry. In the crystal, adjacent mol-ecules are linked through O-H⋯O and O-H⋯N hydrogen bonds involving the sulfate anion and the coordin-ated and uncoordinated water mol-ecules into a three-dimensional network.