Abstract: OBJECTIVE To investigate the spectrum-effect relationship between mid-infrared spectrum(MIR) fingerprint of Hedysari Radix and antioxidant capacity in vitro. METHODS The MIR fingerprints of Hedysari Radix from 12 different regions were collected by FTIR, its antioxidative activity were determined by DPPH method, Person correlation analysis and multivariate nonlinear regression analysis (step-back method) were used to establish the relationship between MIR fingerprint of Hedysari Radix and antioxidant capacity in vitro. RESULTS The decocted solution of Hedysari Radix showed maximum clearance rate of DPPH at concentration of 80 mg·mL^-1. The spectrum-effect relationship equation between MIR fingerprint of Hedysari Radix and antioxidant capacity was Y=57.329X₁-32.913X₃+48.571X₉(P＜0.05, R=0.936). CONCLUSION There is close correlation between MIR fingerprint of Hedysari Radix and antioxidant capacity, and the absorption of 3 378, 2 372, 864 cm^-1 had main effect on antioxidant capacity of Hedysari Radix.