AbstractBlack liquor alkaline lignin and magnesium lignosulfonate were liquefied at 320 oC. The antioxidant abilities of the liquefaction products were compared with the raw materials. Results showed that the total phenol content and unit antioxidant power of both alkaline lignin liquefaction products (ALLP) and magnesium lignosulfonate liquefaction products (MLLP) were improved, and ALLP had a larger increase than MLLP. The influence of reaction time and temperature on oil yield, total phenol content, and antioxidant power of ALLP was evaluated. The total phenol content was found to have certain relationships with the antioxidant abilities. These results explore a new approach for further studies and applications of liquid antioxidant from lignins.