In the title compound, [Cu(C(2)O(4))(C(5)H(8)N(2))(2)(H(2)O)], the Cu(II) atom is coordinated in a slightly distorted square-pyramidal geometry by two N atoms belonging to the two 3,5-dimethyl-1H-pyrazole ligands, two O atoms of the oxalate anion providing an O,O'-chelating coordination mode, and an O atom of the water mol-ecule occupying the apical position. The crystal packing shows a well defined layer structure. Intra-layer connections are realised through a system of hydrogen bonds while the nature of the inter-layer inter-actions is completely hydro-phobic, including no hydrogen-bonding inter-actions.