This study evaluated the formation of chlorinated transformation products during photo-Fenton treatment of pyrimethanil (PYR-20mgL −1 ) in two water matrices, demineralised water (DW) and water containing 5gL −1 of NaCl (DW NaCl ). All experiments were carried out in compound parabolic collectors (CPC) at an initial Fe 2+ concentration of 5mgL −1 and H 2 O 2 concentration of 150–350mgL −1 . Dissolved Organic Carbon (DOC), High-Performance Liquid Chromatography with Diode-Array Detection (HPLC–DAD), Liquid Chromatography–Time-Of-Flight Mass Spectrometry (LC–TOF-MS), toxicity and biodegradability tests were conducted to control the photocatalytic treatment. In DW, PYR was completely eliminated after 11.8min of illumination and initial DOC was reduced 50% after 79min of illumination with 33mM of H 2 O 2 consumed. On the other hand, in DW NaCl water matrix, the same reduction in DOC took 110min of illumination and H 2 O 2 consumption of 39mM, and total degradation of PYR was observed at 12min of illumination. PYR transformation products (TPs) were identified by LC–TOF-MS. It was demonstrated that photo-Fenton in a DW NaCl produces some chlorinated TPs in addition to the non-chlorinated TPs identified during degradation in the DW. All TPs formed were eliminated during photo-Fenton. Additionally, the presence of chlorinated TPs does not increase the toxicity of the water, and TPs formed are more biodegradable than PYR.