Abstract: Phytosterols is a group of natural plant-derived compounds with cholesterol-lowering and other physiological functions. However, the low solubility and low dispersion in water limit their application in the food field. In order to expand the application of phytosterols in low-fat or water-dispersed functional food systems, lipid-based nanoparticles loaded with phytosterols were prepared by emulsion template method combined with ultrasound using glyceryl monostearate as lipid matrix and lecithin as surfactant for the delivery of phytosterols in the water environment. Phytosterols loaded lipid-based nanoparticles were prepared by different ultrasonic treatment (including time and power) and cooling ways, and then the particle size, polydispersity index and Zeta potential of the obtained nanoparticles were measured by dynamic light scattering to optimize the preparation conditions. Subsequently, the effects of surfactant content and phytosterols addition on particle size, polydispersity index, Zeta potential and encapsulation efficiency of nanoparticles were studied. The encapsulation efficiency of the samples was calculated indirectly by determining the content of unencapsulated phytosterols by high performance liquid chromatography. Finally, the microstructure of nanoparticles was observed by transmission electron microscopy and the wettability of freeze-dried samples was studied by measuring the contact angle. The results showed that the samples after ultrasonic treatment showed a semi transparent or even transparent appearance, with particle size of 100-200 nm and zeta potential below -30 mV. The optimized conditions showed that the ultrasonic time of 4 min, the ultrasonic power of 120W, and rapid cooling was conducive to the preparation of phytosterols loaded nanoparticles with smaller particle size and higher negative charge. Meanwhile, polydispersity index data showed that the nanoparticles had good homogeneity, even close to monodisperse system, which was consistent with the observation results of transmission electron microscopy. Surfactant was confirmed to be an important contribution for obtaining more ideal nanoparticles. The structure of phytosterols loaded nanoparticles gradually stabilized from 0.8% of phospholipids addition, and their encapsulation efficiency reached more than 99%. Due to the compatibility of amphiphilic lipid matrix with phytosterols, the encapsulation efficiency of nanoparticles was more than 90% when 100-500 mg of phytosterols were added (the content of emulsifier was 0.8%), achieving a high concentration delivery of phytosterols in water. In addition, the freeze-dried samples also showed excellent water dispersion effect, which facilitated the storage of samples without changing the performance. The above research provides a new idea for the development of functional foods or beverages rich in phytosterols.