The reaction between mononuclear [Ln(bbpen)Cl] [Ln = Gd or Dy; H2bbpen = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine, C28H30N4O2] and potassium oxalate monohydrate in water/methanol produced the solvated centrosymmetric isostructural binuclear (μ-oxalato)bis{[N,N′-bis(2-oxidobenzyl-κO)-N,N′-bis(pyridin-2-ylmethyl-κN)ethylenediamine-κ2 N,N′]dilanthanide(III)}–methanol–water (1/4/4) complexes, [Ln 2(C28H28N4O2)2(C2O4)]·4CH3OH·4H2O, with lanthanide(III) = gadolinium(III) (Ln = Gd) and dysprosium(III) (Ln = Dy), in high yields (ca 70%) directly from the reaction mixtures. In both complexes, the lanthanide ion is eight-coordinate and adopts a distorted square-antiprismatic coordination environment. The triclinic (P\overline{1}) unit cell contains one dimeric unit together with four water and four methanol molecules; in the final structural model, two of each type of solvating molecule refine well. In each lanthanide(III) dimeric molecule, the medium-strength O...H—O hydrogen-bonding pattern involves four oxygen atoms, two of them from the phenolate groups that are `bridged' by one water and one methanol molecule. These interactions seem to contribute to the stabilization of the relatively compact shape of the dimer. Electron densities associated with an additional water and methanol molecule were removed with the SQUEEZE procedure in PLATON [Spek (2015). Acta Cryst. C71, 9–18]. These two new compounds are of interest with respect to magnetic properties.