In the title compound, [KYb(C(2)O(4))(2)(H(2)O)(4)](n), the Yb(III) ion lies on a site of [Formula: see text] symmetry in a dodeca-hedral environment defined by eight O atoms from four oxalate ligands. The K atom lies on a different [Formula: see text] axis and is coordinated by four O atoms from four oxalate ligands and four water O atoms. The oxalate ligand has an inversion center at the mid-point of the C-C bond. The metal ions are linked by the oxalate ligands into a three-dimensional framework. O-H⋯O hydrogen bonding is present in the crystal structure.