Photolytic degradation reactions in aqueous solution of the fungicide triphenyltin hydroxide (TPT), a compound with typical physicochemical properties of a persistent organic pollutant (POP) were investigated. The quantum yield is found to be close to unity, Φ _TPT,254 ±2σ=1.25±0.26 at 254 nm (T=295-298 K). Using nitrobenzene as reference compound the OH-rate constant of TPT was found to be k _OH,TPT ±2σ=(9.4±3)×10 ⁹ M ^-1 s ^-1 at T=295 K. Although the quantum yield of TPT is among the highest values found for a pesticide, the degradation by sunlight is negligible due to a lack of overlap with the UV-spectrum of TPT. Adopting OH-levels of c _OH =2.5 × 10 ^-16 M the OH-rate constant of dissolved TPT leads to a lifetime of about 1 week in surface waters. However, the lifetime found is assumed to be a minimum value and the influence of the adsorption of TPT on particles on degradation reactions in the environment should be investigated.