The photodegradation behavior of bisphenol AF (BPAF) in montmorillonite KSF dispersions was investigated. The influence of KSF dosage, initial BPAF concentration and initial pH on the degradation of BPAF was studied. The main purposes were to clarify the degradation mechanism of BPAF and quantify the fluorine concentration during the degradation. At an initial concentration of 40 μM, more than 78% TOC was removed within 600 min irradiation, and the concentration of fluorine was 0.62 mg L − 1 . Degradation of BPAF followed the Langmuir–Hinshelwood kinetics rate model and the reaction rate constant k re was 0.887 μM min − 1 . Hydroxyl radicals were the main reactive species in the irradiated KSF dispersion. Intermediates of BPAF decomposition were determined by LC–MS analysis.