In this article, amphiphilic starch nanocrystals were synthesized by graft copolymerization of starch nanocrystals with styrene in aqueous emulsion system. The starch nanocrystals of size around 50 nm were used, which were prepared by acid hydrolysis of corn starch. The structure of starch-g-polystyrene nanocrystals was characterized by Fourier transform infrared and H nuclear magnetic resonance (H-1 NMR). The crystalline structure as well as its particle morphology was studied by X-ray diffraction and scanning electron microscopy, respectively. The results indicated that the amphiphilic starch nanocrystals obtained exhibit the size around 80-100 nm. Its crystalline structure is basically not changed after grafting polystyrene suggested that the polystyrene was essentially grafted on the surface of starch nanocrystals. Wettability experiments indicated that the prepared starch-g-polystyrene nanocrystals can be uniformly dispersed both in water phase and oil phase revealing excellent amphiphilicity. (C) 2007 Wiley Periodicals, Inc.