Based on high-pressure homogenisation and complex coacervation, twelve oil-loaded nanocapsule systems for intravenous or peroral administration were developed by conversion of nanoemulsions into nanocapsules, possessing a three-layered solid capsule shell of biocompatible polyelectrolytes. They were physico-chemically characterised using photon correlation spectroscopy, laser diffraction, electron microscopy, field flow fractionation, and zeta potential. Four samples were successful in terms of homogeneous, nanoscaled size, good dispersion stability, and high oil content. With one successful example, shell solidification could be enhanced by increasing the number of shell layers from three to five which was proven by atomic force microscopy and ultrasonic resonator technology. Independent of the layer numbers, polyelectrolyte nanocapsules displayed a fast-releasing dosage form, as electron paramagnetic resonance spectroscopy and ultrafiltration showed. Finally, in vivo investigations of the physiological fate in mice reflected their potential to allow for systemical uptake of encapsulated drugs after peroral application.