It is reported that mixing polyglycerol polyricinoleate (PGPR) and polyglycerol laurilester has a great emulsifying capacity, and consequently fine oil-in-water (o/w) emulsions can be formed. However, the role of PGPR is not clear. The objective of this research is to investigate the phase behavior of vegetable oil/mixture of PGPR and polyglycerol fatty acid ester/water systems, and to clarify the role of PGPR in making a fine emulsion. Phase diagrams were constructed to elucidate the optimal process for preparing fine emulsions. In all the systems examined in this study, the phases, including the liquid crystal phase (L_c) and sponge phase (L₃), spread widely in the phase diagrams. We examined droplet size of the emulsions prepared from each phase and found that o/w nano-emulsions with droplet sizes as small as 50 nm were formed by emulsifying either from a single L₃ phase or a two-phase region, L_c + L₃. These results indicate that a sponge phase L₃ or liquid crystal phase Lc or both is necessary to form an o/w nano-emulsion whose average droplet diameter is less than 50 nm for PGPR and polyglycerin fatty acid ester mixtures used as surfactant.