Abstract: Brewer's spent grains were employed as raw material to prepare protein peptides by solid-state fermentation of Aspergillus oryzae, and the effects of different medium conditions on peptide conversion ratio were studied. The effects of the carbon source type, the amount of carbon source, the amount of potassium dihydrogen phosphate, and the ratio of solid to liquid on the peptide conversion ratio were investigated by single factor experiment, and response surface methodology was used to optimize the medium conditions, the regression equation between the peptide conversion ratio and various influencing factors was established. The results showed that, the optimal conditions for the preparation of brewer's s pent grains protein peptide by Aspergillus oryzae were as follows: Sucrose supplemental level at 4.21%, adding potassium dihydrogen phosphate at 0.51%, and solid-liquid ratio at 1:3（g·mL⁻¹）. Under the condition, the conversion ratio of protein peptides from brewer's spent grains could reach 50.73%. The results can provide a technical reference for the production of protein peptides from brewer's spent grains.