Hydrothermal treatment of lignin was conducted using a batch reactor to obtain phenolic compounds between 260-350 degrees C at various reaction times. It was found that at 320 degrees C, 30 min, the max unit total phenol content of liquid product was obtained. With the 1,1-diphenyl-2-picrylhydrazyl radical method, the antioxidant activity and total phenol content correlated well. The liquid product improved the thermal oxidation stability of tung oil obviously at 130 degrees C. The liquid product is a promising antioxidant at relatively low temperature.