In the crystal structure of the mononuclear title complex, [Ni(C(10)H(9)N(2)O(2))(2)(H(2)O)], the Ni(II) ion is five-coordinated in a distorted square-pyramidal geometry by two N atoms and two O atoms from 2,3-dimethyl-4-oxopyrido[1,2-a]pyrimidin-9-olate ligands and one O atom from a water mol-ecule. O-H⋯O hydrogen bonds between the coordinated water mol-ecule and the ligand connect adjacent mol-ecules, forming a ribbon parallel to the b axis.