Among pharmaceutical products (PPs) recalcitrant to water treatments, diclofenac shows a high toxicity and remains at high concentration in natural aquatic environments. The aim of this study concerns the understanding of the adsorption mechanism of this anionic PP onto an organoclay prepared with a long-alkyl chains cationic surfactant for various experimental pH and temperature conditions. The experimental data obtained by a set of complementary techniques (X-ray diffraction, elemental analyses, gas chromatography coupled with mass spectrometry, and Fourier transform infrared spectroscopy) and the use of Langmuir, Freundlich and Dubinin-Radushkevish equation models, reveal that organoclays show a good affinity to diclofenac while the chemical nature of surfactant appears to play a minor role. This study stresses out the application of organoclays for the adsorption of a recalcitrant PP in numerous aquatic compartments that can be used as a complement with activated carbon for waste water treatment for instance.