The crystal and molecular structure of catena-(bis(μ -oxalic acid)-μ -hydrogen oxalate-di-aqua-sodium(I)) was detect-ed by X-Ray analysis. The compound crystallizes in the triclinic space group P-1, with a(Å) 6.2378(12); b(Å) 7,1115(14); c(Å) 10.489(2); α(°) 94.65(3); β(°) 100.12(3); γ(°) 97.78(3). The so-dium cation in the title compound is eight coordinated and forms a square antiprism. It is surrounded by two molecules of oxalic acid, one hydrogen oxalate anion and one water mole-cule. Both oxalic acid and hydrogen oxalate anion act as poly-dentate bridging ligands. Centrosymmetric sodium cations are bounded by hydrogen oxalate anions through a system of H bonds involving the molecules of oxalic acid. In the lattice, the 3D structure stabilized by H bonds is formed.Supporting information: X-Ray (CIF file)