The novel coordination polymer of general formula {[(H₂O)Ba(μ-H₂O)Ba(OH₂)₄]@ [(C₂O₄)₂Al(μ-OH)₂Al(C₂O₄)₂].H₂O}n (1), has been synthesized in water and characterized by FTIR spectra, elemental and thermal analyses, and by full X-ray structure determination. Compound 1 crystallizes in an interesting nonmolecular coordination network where oxalato ligands μ-bridge neighboring Ba(II) and Al(III) centers. The asymmetric unit of 1 consists of one cationic tri-μ-oxygen-bridged pseudo-dimer - formally [(H₂O)Ba1(μ-H₂O)Ba2(OH₂)₄]⁴⁺ - one centrosymmetric anionic di-μ-hydroxido-bis[cis-bis(oxalato)aluminate] dimer - [(C₂O₄)₂Al1(μ-OH) ₂Al2(C₂O₄)₂]^4- - and one solvent water molecule. The Ba²⁺ ions in the cationic dimer are both ten-coordinate and 4.335(1) Å apart. The Al³⁺ ions in the anionic dimer each experience distorted octahedral coordination by six O atoms, being distant by 2.854 Å in average and centered at two independent lattice positions related by the P2₁/n space group symmetry. The anionic dimers are interconnected amongst themselves via O-H***O bridgings across the hydroxido groups into 1-D pillars that run parallel to [001]. These negatively charged pillars are tightly cross-linked via coordinate bonds of oxalato O atoms to the cationic Ba dimers. Coulombic interactions between the ionic motifs and extended 3-dimensional H-bonding involving solvent water molecules as well, concur to consolidate the bulk structure. Thermogravimetric analysis (TGA) shows that compound 1 is stable to heat up to 400 °C.