A composition comprises an aqueous dispersion of particles (p) of mean hydrodynamic diameter between 50 and 5000 nm. The particles contain (A) polymers based on cyclodextrin units, comprising on average at least four cyclodextrin units within their structure; and (B) macromolecules of polysaccharides comprising groups G capable of forming inclusion complexes with the cyclodextrins present in the structure of the polymers (A), with an average number of groups G per polysaccharide macromolecule at least equal to three. The compounds (A) and (B) are water-soluble in the isolated state. A method is also provided which relates to the preparation of these compositions, as well as their use in order to achieve the encapsulation of compounds such as active substances.