Nature of structuring of aqueous solutions of paramagnetic endofullerenols Gd@Cn(OH)38–40 was determined in relation to the concentration and pH factor from small-angle neutron scattering, viscometric, and conductometric data . Molecular fractal clusters of the type of branched polymers were found, with their correlation radius being about 20 nm and aggregation numbers reaching a value of 104. The clusterized systems obtained are promising as a basis for MRI-contrasting agents and other biomedical preparations for diagnostics and therapy.