Objective To evaluate the antioxidant activities of different chemical constituents from Astragalus mongholicus Bunge and their protection against xanthine (XA)/xanthine oxidase (XO)-induced toxicity in PC12 cells. Methods The compounds of Astragalus mongholicus Bunge were isolated by chromatography and the structures were elucidated on the basis of spectral data interpretation. Their antioxidant activities were detected by 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities in a cell-free system. Meanwhile, the effects against XA/XO-induced toxicity were assessed using MTT assay in PC12 cells. Results Ten principal constituents were isolated and identified as formononetin (I), ononin (II), calycosin (III), calycosin-7-O-β-D-glucoside (IV), 9,10-dimethoxypterocarpan-3-O-β-D-glucoside (V), adenosine (VI), pinitol (VII), daucosterol (VIII), β-sitoster (IX) and saccharose (X) from Astragalus mongholicus Bunge. The compounds I, III, and IV scavenged DPPH free radicals in vitro. Formononetin and calycosin were found to inhibit XA/XO-induced cell injury significantly, with an estimated EC50 of 50 ng/mL. Conclusion Compound Ⅱ, Ⅵ, and Ⅶ are first reported in this plant. Calycosin exhibits the most potent antioxidant activity both in the cell-free system and in the cell system. Objective To evaluate the antios activities of different chemical constituents from Astragalus mongholicus Bunge and their protection against xanthine (XA)/xanthine oxidase (XO)-induced toxicity in PC12 cells. Methods The compounds of Astragalus mongholicus Bunge were isolated by chromatography and the structures were Butlucidated on the basis of spectral data interpretation. They antioxidant activities were detected by 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities in a cell-free system. at the same time, the effects against XA/XO-induced Using MTT assay in PC12 cells. Results Ten principal constituents were isolated and identified as formononetin (I), ononin (II), calycosin (III), calycosin-7-O-β-D-glucoside (IV), 9,10- dimethoxypterocarpan-3-O-β-D-glucoside (V), adenosine (VI), pinitol (VII), daucosterol (VIII), β-sitoster (IX) and saccharose (X) from Astragalus mongholicus Bunge. The compounds I, III, and IV scavenged DPPH free radicals in In vitro. Formononetin and calycosin were found to inhibit XA/XO-induced cell injury significantly, with an estimated EC50 of 50 ng/mL. Conclusions Compound II, VI, and VII are first reported in this plant. Calycosin exhibits the most potent antioxidant activity Both in the cell-free system and in the cell system.