Abstract: In order to investigate the changes of components and biological activities of Auricularia auricula liquid after enzymatic hydrolysis and fermentation, the Auricularia auricula liquid was firstly subjected to enzymatic hydrolysis using cellulase and pectinase, followed by joint fermentation using Lactobacillus plantarum and Lactobacillus fermentum with inoculation ratio of 1:1. The components of the Auricularia auricula liquid before and after enzymatic hydrolysis and fermentation treatment was monitored. Their structure was characterized by Fourier infrared spectrum (FTIR) and atomic force microscopy (AFM). The antioxidant activity, anti-α amylase and anti-α- glucosidase activities in vitro were evaluated. The oxidative damage model of RAW264.7 cells induced by H₂O₂ was established, and the protective effect of different concentrations of Auricularia auricula fermentation broth on cell oxidative damage was evaluated by detecting the content of antioxidant enzymes. The effects of the fermentation broth on RAW264.7 cell proliferation, phagocytosis and cytokine release were also determined. Results showed that the total sugar content in the fermentation broth of Auricularia auricula increased to 539.14 mg∙g⁻¹ from 170.57 mg∙g⁻¹ in the untreated Auricularia auricula liquid, and the protein content increased from 15.00 mg∙g⁻¹ in the untreated Auricularia auricula liquid to 81.28 mg∙g⁻¹ simultaneously. The FTIR suggested that there were significant increase in -OH vibrations of polysaccharide in Auricularia auricula liquid after enzymatic hydrolysis and fermentation treatment. The results of atomic force microscope showed that the three-dimensional structure of the fermentation broth of Auricularia auricula was in dense grain piles-like structure, and the polysaccharides in Auricularia auricula were hydrolyzed to produce more small molecules of sugars, and the content of branched chains increased and agglomerated. Compared with the untreated Auricularia auricula liquid, the α-amylase inhibition rate of the Auricularia auricula fermentation broth increased by 2.39 times when the concentration was 0.5 mg/mL. And 5 mg/mL of Auricularia auricula fermentation broth increased the bile salt binding capacity by 1.37 and 2.66 times of the Auricularia auricula hydrolysate and untreated Auricularia auricula liquid. The fermentation broth improved the proliferation and phagocytosis of RAW264.7 cells and showed protective effect on oxidative damaged cells. The jointed treatment by enzymatic hydrolysis and fermentation greatly improved the functions of the active components of Auricularia auricula, which provided a theoretical basis for the further development and research of Auricularia auricula products.