Fe-57 Mossbauer measurements have been performed on the lamellar iron (II) ethylphosphonate Fe(II)(C2H5PO3). H2O. Mossbauer parameters have been studied as a function of temperature in the paramagnetic state (above 28 K). In the temperature range 150-200 K this compound has been found to undergo a phase transition resulting in a discontinuity in the quadrupole splitting Delta E. This unusual behavior was ascribed to a structural change and not to a transition from an ordered to a quasi-liquid state of the water molecule and/or CH2-CH3 moieties, Results of a preliminary infrared study supports this hypothesis.