Abstract: Cassava starch nanoparticles, Guangxi specialty resources cassava native starch as raw material, were prepared by precipitation method with the aid of microwave and ultrasound.The effects of starch milk concentration, volume ratio of starch solution to absolute ethanol, dropping rate of starch solution, the power of microwave ultrasonic, the time of microwave ultrasonic, the microwave ultrasonic power in the starch solution drop process on starch nanoparticle size and polydispersity index were investigated by dynamic light scattering technique.Therefore, the optimal conditions for the preparation of cassava starch nanoparticles were obtained:The starch milk concentration was 20 mg/mL, the power of microwave ultrasonic was 24:500 W:W, the time of microwave ultrasonic was 50 min, the feed-to-alcohol ratio was 1:8, the dropping rate of starch solution was 20 mL/min and the microwave ultrasonic power in the process of adding starch solution was 24:300 W:W.Fourier transform infrared spectroscopy, field emission scanning electron microscope, X-ray diffraction were used to characterize the cassava native starch and cassava starch nanoparticles. The physicochemical properties of starch nanoparticles such as solubility, swelling degree, water absorption and oil absorption were studied.The results showed that cassava starch nanoparticles had good spherical morphology and the size distribution was uniform.The crystal type of cassava starch nanoparticles changed from A type to V type, and the relative crystallinity decreased significantly.Compared with cassava native starch, the solubility of starch nanoparticles increased from 0.9% to 78.3%, the degree of swelling increased from 4.166% to 10.86%, the oil absorption rate increased by 170%, the water absorption rate increased by 3.1% within 12 hours, and the cassava starch nanoparticles had good dispersibility in aqueous solution.The starch nanoparticles had high application value which can be used in food pigments, spices, seasonings, vitamins, oils and other products.