Poly (n-butylcyanocrylate) nanocapsules were obtained by interfacial polymerization from a water-in-oil microemulsion. The latter was composed of pharmaceutically acceptable excipients such as Labrafac lipophile WL 1349 (oil), Plurol oleique CC497 (surfactant), and Labrasol (co-surfactant) and was able to incorporate 20% aqueous phase. Pure n-butylcyanoacrylate monomer (without any dilution in a halogenated solvent) was added to the microemulsion in order to obtain an oily suspension of biocompatible and biodegradable aqueous core nanocapsules. Finally, in order to provide a direct evidence of the presence of water within the nanocapsules, a mass balance and nuclear magnetic resonance analysis were performed. The results showed that the presence of water and transmission electronic microscopy confirmed a hybrid structure of the final nanosystem, between a genuine nanocapsule and a matrix system: a nanosystem with multicavities filled with water.