In this article a facile way of producing starch-based nanoparticles (SNPs) with high yields and predictable size by an alkali-freezing treatment is presented. A new mix solvent, sodium hydroxide–urea aqueous solution, has been developed to disperse corn starch. After refreezing, thawing, stirring at room temperature and dialysis, resultant aqueous suspensions of SNPs are obtained and characterized using a scanning electron microscope (SEM) and dynamic light scattering (DLS) to learn the particle morphology, mean size and size distribution. By adjusting parameters such as the sodium hydroxide : urea ratio and temperature, the size of particles can be controlled from micro- to nanometer. Furthermore, this process that leads to the nanoparticles causes no changes in the structures of the starch granules as characterized by IR or ¹H-NMR. Freeze-dried SNPs were found to be amorphous as revealed by wide-angle X-ray diffraction (WAXD).