A surface-active monomer, polyisobutylene-succinimide pentamine (Lubrizol U), was used as a stabilizer for synthesizing polyurea nanocapsules with aqueous core via polyaddition at inverse miniemulsion droplet interface. Because of the presence of amine groups in the Lubrizol molecule, it is covalently incorporated into the polymeric interfacial layer after reaction, resulting in more compact (less permeable) capsule shell. The influence of the stabilizer and the monomer concentration oil the shell thickness, colloidal stability, average capsule size, and capsule size polydispersity were examined in detail. Different materials, Such as a water-soluble fluorescent dye and aqueous dispersion of magnetite nanoparticles with 10 rim in size, were used as inner phase of the polyurea capsules. The encapsulation efficiency was studied using fluorescein its a marker. As all example for biomedical application, the fluorescein-containing capsules were utilized in cell uptake experiments and Visualized using fluorescence microscopy.