Lignin was extracted from Acanthopanax senticosus remainders after pharmaceutical production process, with acetic acid-water as extracting reagent. Four factors effects, namely reaction temperature from 160°C to 220°C, reaction time from 40 min to 100 min, acetic acid concentration from 50% to 80% and solid-liquid ratio from 1:40 to 1:5, were studied and optimized by a four-level orthogonal array design (OAD) on lignin antioxidant capacity. The results indicated the reaction temperature and reaction time were significant factors among these factors. At the same lignin solution concentration, the acetic acid lignin antioxidant capacity was better than that of Kraft lignin, but much lower than that of butylated hydroxyanisole (BHA).