The invention relates to a composition which makes it possible to obtain a gelled aqueous foam capable of decontaminating, stripping or degreasing a surface. The composition of the present invention comprises one or more surfactants, one or more acidic or basic reactants and a gelling agent.The decontamination foam obtained from this composition exhibits long lifetimes, generally of between 1 and 10 hours, guaranteeing a prolonged time of action on the surface and a high decontamination effectiveness. These foams can be used to remove the radioactivity from an inaccessible plant, which is large in size and complex in design, by simple filling or by simple spraying over an accessible surface.