To obtain new information on the properties of humic acids (fractions of humic substances), we have studied the fluorescence and photochemical properties of various samples of humic acids alone and the photodegradation of phenolic ecotoxicants in the presence of humic acids. The influence of different light sources and wavelengths of the exciting radiation has been studied, as well as the capability of humic acids to affect the photolysis in different ways depending on their origin.