From the 1960s to the 1990s, the large-scale production of banana in the French West Indies involved an intensive use of chlorinated pesticides, such as chlordecone (CLD) and beta-hexachlorocyclohexane (β-HCH), resulting in the diffuse contamination of soil and surface waters in the banana-producing areas. Due to its strong persistence in natural environments, its high resistance to chemical reactions and microbiological degradations, around 8–9% of the cultivation areas of Guadeloupe contain CLD and β- HCH at concentrations higher than 1 mg/kg in topsoil, and some banana fields exhibit content higher than 9 mg/kg. Conventional technologies for water decontamination and wastewaters treatment like biological processes or adsorption on activated carbon do not guarantee remediation of these recalcitrant substances or do not provide an ultimate solution. On the other hand, advanced oxidation processes that involve "in situ" formation of free radicals have become of special interest in the last years. The efficiency of modern oxidation technologies like photo-Fenton process has been assessed for the degradation of several classes of pesticides and refractory compounds. In this work, degradation of CLD and β-HCH in aqueous solution by photolysis (using medium pressure mercury lamp), Fenton and photo-Fenton processes was studied. Several analytical approaches were evaluated for the monitoring of CLD and β-HCH concentration-time profiles in very dilute conditions (down to 0.1 mg.L-1). At last two techniques gave convenient results: liquid chromatography-tandem mass spectrometry (LC-MS/MS) with APCI ion source and gas chromatography- mass spectrometry (GC-MS). Unlike GC-MS/MS, LC-MS/MS analysis needs frequent calibration due to complex matrix effects (presence of dissolved iron, quenching agents …) but the sample can be analyzed without any pretreatment, whereas water should be removed prior to GC-MS/MS analysis. Fenton oxidation did not yield significant conversion of CLD, and best results were obtained with photolysis, where 64% of the pesticide was removed after 5 hours. Conversion of β-HCH by photolysis reached 90% in 5 hours, but despite Fenton oxidation could also efficiently degrade this molecule, combination of UV irradiation with hydrogen peroxide and ferrous iron did not show any significant improvement.