ObjectiveTo improve the efficacy of Astragalus membranaceus (Fisch.) Bunge (A. membranaceus, Huang Qi), and to further develop and utilize it, fermentation technology was applied to the stem and leaf of A. membranaceus to enhance its immune function.MethodsIn this study, we fermented A. membranaceus stem and leaf (ASL) with probiotics and investigated its immune function. Firstly, we screened suitable strains for ASL fermentation and optimized the fermentation process. Secondly, we determined the antioxidant capacity of fermented ASL and its effect on inflammation in mouse monocyte-macrophage cell. Finally, the immunocompromised mice were treated with fermented ASL to investigate the changes in their immune ability.ResultsAmong the 10 selected probiotics, Lactobacillus plantarum was the most suitable strain for ASL fermentation. After optimization of the fermentation process, the content of saponins in fermented ASL was significantly increased. The fermented ASL exhibited strong anti-inflammatory and antioxidant activities in vitro. The in vivo immune efficacy improved by promoting the development of the spleen and thymus, as well as raising the immunoglobulin M, tumor necrosis factor-α, and interleukin-1β levels of in the serum.ConclusionThis study contributes to developing the non-medicinal parts of A. membranaceus, expands its medicinal resources, highlights the potential of fermentation technology to enhance these parts, and provides a reference for further development. Based on this approach, we can promote using non-medicinal parts of herbal medicines, minimize drug waste, and offer a reference for developing non-medicinal components in Chinese herbal medicines.