Abstract: Emodin was one of the main active ingredients in Chinese Traditional Herb Medicine of rhubarb with hydrophobicity. However, emodin had poor water solubility, which was improved by loading in a certain matrix. In this study, the microcapsules of emodin-casein complexes were prepared with casein as matrix with ultrasound treatment. The structural properties of the complexes were analyzed by fluorescence spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy. The thermal properties, DPPH and ABTS⁺ free radical scavenging activities of the complexes were measured. In addition, the release profiles of emodin from the complexes were evaluated by simulated gastrointestinal digestion experiment. The results showed that the ultrasound treatment within 1~3 min duration had not significant effect on the fluorescence properties of the complexes with the addition of emodin at 8~10 μg/mg. Furthermore, there were not significant effect of ultrasound treatment on the FTIR spectra and morphology of emodin-casein complexes. In addition, the DPPH free radical scavenging activity of the complexes had the lowest value with 1 min-ultrasound treatment, but the highest value of ABTS⁺ free radical scavenging activity among other samples with the same emodin addition. The release rate of emodin from the emodin-casein complexes during simulated gastrointestinal digestion was improved by 1 min-ultrasound treatment, but retarded by 5 min-ultrasound treatment. The results could provide references for the application of ultrasound treatment in the properties’ regulation of emodin-casein complexes.