In recent years, the solution enhanced dispersion in supercritical fluids (SEDS) technique is widely applied to produce fine and small particles of drugs and other active ingredients. However, this technique still cannot be used to generate particles in the submicrometer range for specific compounds, such as carotenoids. In this study, a modified SEDS technique is explored and applied in the preparation of beta-carotene nanoparticles with relatively narrow size distribution. This novel technique, termed SEDS-EM, combines a traditional SEDS technique with ultrasonication from the supercritical antisolvent with enhanced mass transfer precipitation technique (SAS-EM). For this new technique, the beta-carotene solution is premixed with the antisolvent (supercritical CO2) in a coaxial nozzle; then the mixed solution is sprayed from the coaxial nozzle onto a surface vibrating at an ultrasonic frequency. The solution jet is dispersed by the coaxial nozzle and further atomized into very small droplets by the ultrasonic vibrating surface. This combination of a coaxial nozzle and the ultrasound field enhances the mass transfer between the solution and the antisolvent. The resultant beta-carotene particles decreased in size from the micrometer range (2-5 mu m) by SEDS to the nanometer range (20-205 nm) by SEDS-EM. This smaller particle size can be controlled by the power supplied from the attached ultrasound transducer utilized in SEDS-EM. The size and morphology of the particles are observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the process parameters on the beta-carotene yield are discussed. The crystallography transformation of the processed and unprocessed beta-carotene is characterized by XRD and FTIR. The particle precipitation in sub and near critical regions of the DCM-CO2 binary system is also discussed.