A common method used to prepare polymeric nanoparticles in pharmaceutical technology is emulsion-diffusion. However, this method has several disadvantages due to the long duration of the process. At the diffusion step of conventional emulsion-diffusion, high pressure treatment could replace the addition of great quantities of water resulting in diffusion of the solvents from the internal phase to the external phase. The objective of the present study was to develop a novel method for nanoparticle formulation by combining high pressure treatment with the emulsion-diffusion method to avoid an additional diffusion step in the aqueous phase. After emulsification at 11,000 rpm, the emulsions were pressurized at 100, 200 and 300 Mpa, each for 300, 600, 900 or 1200 s. The mean size and morphology of the nanoparticles were analysed by Mastersizer, TEM and SEM. The mean size of pressurized emulsion nanoparticles was the same at 100 MPa for holding times up to 600 s. Also, the pressurized emulsion nanoparticle size increased and the peak and width of the size distribution curve was higher and slightly narrower depending on the pressure and the holding time. This study shows that pressure treatment can produce polymer membranes surrounding the oil surface owing to the precipitation of PCL, inducing the diffusion of solvent from the interior to the exterior based on TEM images. From these results, it is believed that high pressure treatment should be considered as a successful alternative for preparing nanoparticles.