The degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) under UV light was studied under various conditions. A photoreactor was used for the photochemical reaction. Calibration curves for 2,4-D were generated at two different absorption maxima (230 and 283 nm). The effects of various parameters such as light intensity, exposure time, various solvents (10% methanol and 10% acetonitrile) and micellar media (cationic and anionic) and the effects of some other parameters such as 02, wavelength of light, pH, other commonly occurring ions (e.,g. Cl-, SO42-, Ca2+/Mg2+, Fe3+, NO3-) were studied. The percentage of degradation of 2,4-D was achieved up to 81% in simple aqueous medium. But in cetyltrimethyl ammonium chloride (CTAC, a cationic micelle) the percent degradation can even be further increased. The percent degradation of 2,4-D using solar irradiation under similar conditions as that applied for the photoreaction using the photoreactor was compared. Using the solar light the degradation was very negligible. The reaction in general follows zero-order kinetics. But in CTAC micelle the reaction follows first-order kinetics. (C) 2005 Elsevier B.V. All rights reserved.