In the title complex, [Mg(C(2)H(3)O(3))(H(2)O)(4)]NO(3), the Mg(II) cation is hexa-coordinated by four O atoms from water mol-ecules and two O atoms from a 2-hy-droxy-acetate ligand in a distorted octa-hedral coordination geometry. The structure exhibits a three-dimensional supra-molecular network, which is stabilized by nine different O-H⋯O hydrogen bonds.