The thermal stability of metal phosphonate Langmuir-Blodgett (LB) films formed from the amphiphiles octadecylphosphonic acid (OPA) and an azobenzene-derivatized phosphonic acid, (4-(4＇-tetradecyloxyphenyldiazenyl)phenyl)butylphosphonic acid (A4), with divalent and trivalent metal ions has been examined. These films are characterized by the formation of a metal phosphonate continuous lattice in the polar region of the transferred bilayers. The behavior of the films upon heating and with temperature cycling was studied with attenuated total reflectance (ATR)-FTIR, transmission FTIR, absorbance spectroscopy, and X-ray diffraction. A reversible transition is observed between 40 and 50 degrees C in each film, and this process is assigned as a premelting transition in analogy to similar transitions observed in previously studied LB films. Irreversible disordering of the organic networks is observed for each film at higher temperatures, occurring near 150 degrees C in the lanthanum octadecylphosphonate film, near 140 degrees C in the manganese octadecylphosphonate film, and near 120 degrees C in lanthanide films of A4. Despite disordering of the organic network, FTIR and X-ray diffraction indicate that the inorganic network remains intact to above 180 degrees C. The inorganic continuous lattice network is shown to greatly enhance the thermal stability of the metal phosphonate LB films relative to that of the traditional carboxylic acid-based films.