Fifteen isostructural rare earth metal squarates incorporating ethylene glycol ligand with the formula RE(C₄O₄)_1.5(C₂H₆O₂) (RE = Y, La–Nd, Sm–Lu) have been synthesized under hydrothermal conditions and structurally characterized by single-crystal and powder X-ray diffraction, ¹³C CPMAS NMR, absorption spectroscopy, and magnetic susceptibility. A variable-temperature in situ powder X-ray diffraction study on the Ce compound was also performed to determine its thermal stability. Each RE³⁺ cation in the structure is bonded to six squarate anions and one neutral ethylene glycol chelate, and each C₄O₄²⁻ anion coordinates to four RE³⁺ cations such that a new 3-D framework is formed. They are the first examples of organic–inorganic hybrids which contain both squarate and ethylene glycol ligands.