The scale-up of oil-containing polyamide nanocapsules produced by simultaneous interfacial polycondensation and solvent diffusion was successfully achieved. Up to 1500 mL were produced by using a Y-shaped mixer device. The sizes of nanocapsules containing olive oil were modulated from 646 to 211 nm by changing process parameters without modification of the formulation composition. All the results of nanocapsule diameters (dsc) expressed as a function of the Reynolds number (Re) showed the existence of a typical power–law relationship. It was demonstrated that the high turbulences created upon nanocapsule formation are the most important parameter allowing to nanocapsule size to be controlled without modifying the formulation composition. Finally, the power–law relationship was used to predict the size of nanocapsules composed of polyamide or polyester and loaded with Parsol® MCX. The physico-chemical properties of both polyamide and polyester nanocapsules at the laboratory scale were compared to the ones obtained at the pilot scale. The encapsulation efficiency was higher than 98% in both types of nanocapsules at the laboratory and the pilot scales. The in vitro releases of Parsol® MCX from polyester nanocapsules were reproducible at both scales. This is the first time such a power–law was described for the preparation of nanocapsules by interfacial polycondensation and solvent diffusion.