Abstract: Lignin was extracted from the Acanthopanax senticosus remainders, coming from pharmaceutical production process, with 1,4-butanediol as an extracting reagent. The supercritical antisolvent (SAS) process was studied to prepare nanoscale lignin and test its antioxidant capacity. The optimal condition by a four-level orthogonal design is as follows: precipitation temperature 35℃, precipitation pressure 30 MPa, temperature difference +10℃ and concentration of lignin solution 0.5 mg/mL. Nanoscale organic lignin with mean particle size of (0.144±0.03) μm was obtained by verification experiments. The EC50 of the nanoscale and non-nanoscale organic lignin on DPPH was (0.563±0.02) mg/mL and (0.884±0.02) mg/mL, respectively. The results indicated that the DPPH scavenging capacity of nanoscale organic lignin is more improved than that of non-nanoscale organic lignin.