This project target aim to investigate the hydrolysis of fungicide chlorothalonil at different pH solutions at (pH4, pH7, and pH9), as well as its stability under exposure to different temperature degrees and direct exposure to sunlight, and to estimate the photoproducts degradation of chlorothalonil using GC/MS. The data showed that chlorothalonil dissipation from different pH solutions increased more rapidly with increasing both pH value and temperature when compared to acidic and neutral solutions, and that tested pesticides were hydrolyzed more rapidly in alkaline media (PH9) than the other tested pH values at all tested temperatures. The percentage of pesticides that decompose steadily increases and is positively connected with exposure times, according to the data. The results also demonstrated that after 336 hours of exposure to direct sunlight, no detectable level of the pesticides tested was found. The compound (4-hydroxy-2,5,6-trichloroisophthalonitrile) was identified as a major metabolites in environmental samples after photo-degradation products were investigated using GC/MS following exposure to direct sunlight.