In this study, alpha-tocopherol (alpha-T) was dispersed by cosonication with soybean phosphatidylcholine (PC). The particle size in the dispersion was increased to 250 nm up to the alpha-T mole fraction (X-T) 0.4. At X-T = 0.5, the alpha-T/PC mixture was difficult to disperse and the macroscopic oil/water phase separation was observed. By the addition of soybean oil (SO) to alpha-T (molar ratio alpha-T:SO = 1:1), stable aqueous dispersions (diameter 50-70 nm) were obtained in the mole fraction range for the alpha-T and SO mixture (X-M) 0.1-0.8. In order to clarify the dispersal mechanism, the dispersed particles were characterized and the interaction among alpha-T, SO, and PC was investigated using several physicochemical techniques. The trapped aqueous volume inside the alpha-T/PC particles was determined using the aqueous space marker calcein, and this volume was increased with the addition of alpha-T into small unilamellar vesicles of PC. The trapped aqueous volume of alpha-T/SO/PC particles was decreased remarkably with an increase in X-M, and the decline in the fraction of vesicular particles was also confirmed by fluorescence quenching of N-dansylhexadecylamine in the PC membrane by the addition of the quencher CuSO4. These results indicate that the interaction of alpha-T. With PC bilayers and the structure of the alpha-T/PC mixture will be changed by the addition of SO.