Solid lipid nanoparticles (SLN) of fatty acids (FAs) were prepared with a new, solvent-free technique based on FAs precipitation from their sodium salt micelles in the presence of polymeric non-ionic surfactants: this technique was called 'coacervation'. Myristic, palmitic, stearic, arachidic and behenic acid were employed as lipid matrixes. Spherical shaped nanoparticles with mean diameters ranging from 250 to approximately 500 nm were obtained. Different aqueous acidifying solutions were used to precipitate various FAs from their sodium salt micellar solution. Good encapsulation efficiency of Nile Red, a lipophilic model dye, in stearic acid nanoparticles was obtained. The coacervation method seems to be a potentially suitable technique to prepare close to monodisperse nanoparticles for drug delivery purposes.