Currently, polymeric nanoparticles are widely used in a wide variety of biomedical applications, which requires different nanoparticle sizes. Their preparation by solvent evaporation from polymeric nano-emulsions has been described as an appropriate methodology. Nano-emulsions can be prepared by the phase inversion composition method, a low-energy emulsification method, apt for biomedical applications since it can be performed at low conditions. Using this methodology, nano-emulsions droplets and resulting nanoparticle properties depend on the selected components. Many studies have been performed varying some of them. In this work, a specific study has been performed for the first time to find out the effect that the presence of electrolytes in the aqueous phase of the template nano-emulsion has on nano-emulsion and nanoparticle physicochemical properties. PLGA nano-emulsions were prepared using the system: aqueous solution (W)/polysorbate 80 (S)/[4 wt% PLGA in ethyl acetate] (O). The addition of increasing concentrations of electrolytes (PBS) in the aqueous phase produced a decrease on droplet hydrodynamic radii from around 200 nm to around 35 nm. Nanoparticle sizes were determined by the droplet sizes of their template nano-emulsions. Nanoparticles dialysis to an electrolyte solution of 0.16 M, required for many biomedical applications to accomplish the physiological pH and osmolality, did not produce changes in nanoparticle sizes. Therefore, it has been demonstrated for the first time that nano-emulsion and nanoparticle size can be tuned by only varying the electrolyte concentration of the template nano-emulsions. Nano-emulsion templating is a versatile technology that enables the obtaining of tunable nanoparticle sizes; appropriate for a wide range of biomedical applications.