Abstract: The present invention relates to the utilization of algae extracts obtained by extraction in liquid phase, or of at least one active substance isolated from such an extract or obtained by chemical synthesis, selected in particular among the fucols, polyfucols, diphloretols, polyphloretols, bifuhalols, polyfuhalols, phloretols, for the preparation of pharmaceutical, cosmetic, food or agricultural compositions with an anti-radical activity, particularly towards the superoxide radical. The algae used are brown, green or red macroscopic algae and in particular Fucus vesiculosus.