The decomposition of dimethyl methylphosphonate (DMMP) in titanium dioxide and zinc oxide dispersions under simulated solar light has been investigated. DMMP is of interest as a model compound for nerve gas agents. Gas chromatographic analysis for the remaining DMMP and degradation products was used to monitor reaction progress. Reaction conditions were varied to optimize the degradation rate of DMMP and determine the effect on oxidation products. Variables studied include semiconductor loading, solution additives, suspended solids, dissolved oxygen and mixing. The experimental data were fit to predictive equations for overall DMMP degradation rate.