Organophosphorus compounds, becoming the most commonly used pesticides in agriculture, are garnering more interest to be environment and health issues associated with their usage. These compounds run-off into surface water and leach into groundwater supplies where they have been detected. Dyfonate is commonly applied to the soil as an insecticide for the control of variety of insects. However, critical information on the transformation of dyfonate into its hydrolytic byproducts during water treatment is lacking, even though they have been used in the field for a long time. In this study, dyfonate hydrolysis at elevated pH levels, simulating a water treatment operation or similar process, was investigated. Dyfonate, an organophosphorus insecticide used to treat infestations primarily on corn, was investigated due to its greater rate of hydrolysis observed during our screening studies. The hydrolysis of dyfonate was investigated at pH 10, 11, and 12 in phosphate buffered water over the course of 7 days. Two hydrolysis products, thiophenol and phenyl disulfide, were detected. Dyfonate and thiophenol were analysed using high pressure liquid chromatography/UV detection (HPLC/UV), while phenyl disulfide was detected using gas chromatography/mass spectrometry (GC/MS). The relative concentration profiles of dyfonate and its hydrolysis products, as well as their transformation pathways, were also reported. The data from this study will help environmental researchers understanding the hydrolytic pathways of dyfonate and its metabolites at different pHs in a water treatment system.