The photooxidation of dimethyl methylphosphonate (DMMP) on powdered TiO2 has been studied using UV irradiation in the range 2.1 eV to 5.0 eV. It has been found that the P-CH3 and the P-OCH3 moieties are destroyed together by photooxidation, producing adsorbed CO and CO2 as well as formate ions and water. By working at 200 K the photooxidation process has been studied alone, whereas at room temperature both hydrolysis and photooxidation will occur together. An adsorbed PO3 species is the final phosphorus-containing photooxidation product. High coverages of DMMP are not photooxidized due to site blockage for O-2 adsorption on the TiO2 surface.