Abstract: Under low-pressure mercury lamps, a photochemical degradation study of hexaconazole was carried out. The results showed that hexaconazole decomposed rapidly when it was irradiated with 254 nm light, but the photodegradation was not observed with 365 nm light. Photochemical degradation rate of hexaconazole depends on different solvent. The order of photochemical degradation rate in different solvent is methanol>n-hexane>ethyl acetate>water>acetone. Photocatalysts such as FeCl3, H2O2, β-cyclodextrin(β-CyD), FeCl3-H2O2 can enhance photolysis of hexaconazole in aqueous solution. Under experimental conditions, FeCl3-H2O2 is more sensitive than β-CyD, and further still than H2O2 and FeCl3. From the experiments, it was assumed that mechanism of photochemical degradation of hexaconazole in aqueous solution is a photolysis by hydroxyl radical (HO ·).