In the title compound, {[Mn(C(14)H(16)N(5)O(3))(2)]·2H(2)O}(n), the Mn(II) atom (site symmetry ) exhibits a distorted trans-MnN(2)O(4) octa-hedral geometry defined by two monodentate N-bonded and two bidentate O,O'-bonded 8-ethyl-5-oxo-2-(piperazin-1-yl)-5,8-dihydro-pyrido[2,3-d]pyrimidine-6-carboxyl-ate anions. An N-H⋯O hydrogen bond is present in the crystal structure. The extended two-dimensional structure is a square grid and the disordered uncoordinated water mol-ecules occupy cavities within the grid.