The title complex, {[Pr₄(C₂H₃O₂)₁₀(C₂O₄)(H₂O)₂]·2H₂O}_n, was synthesized under hydrothermal conditions from praseodymium acetate and the ionic liquid 1-butyl-3-methylimidazolium chloride via an in situ oxalate-ligand synthesis. The compound is a two-dimensional polymer and in the structure presents tightly bound planes parallel to (100), which are in turn linked into a three-dimensional network by hydrogen bonds involving both coordinated and solvent water molecules. The oxalate anion lies across an inversion centre and acts as a bridge between pairs of Pr atoms within a tetranuclear segment of the polymer.