The interaction of dilute solutions of dimethyl methylphosphonate (DMMP) in H2O with thin porous layers of gamma-Al2O3 has been studied under steady-state conditions using infrared multiple-internal-reflection spectroscopy. Upon the initial introduction of the DMMP solution to a previously H2O-saturated surface, DMMP diffuses into the porous layer and displaces weakly hydrogen-bonded H2O molecules. This is accompanied by hydrolysis of the gamma-Al2O3 to form Al(OH)(3) and/or AlO(OH). The P=O group of DMMP interacts predominantly with H2O and gives no clear indication of bonding to the oxide surface itself, from which it is inferred that the displacement of weakly adsorbed H2O results from the interaction of acidic Al-OH sites with the methoxy O atoms of DMMP. No hydrolysis of the DMMP, either in solution or in contact with the oxide, was detectable under the present conditions. The results have practical implications in the decontamination of materials following exposure to toxic reagents related to DMMP.