Abstract: The ethanol extract from Polygonum cuspidatum Sieb. et Zucc. by hot reflux extraction inhibited radial growth to Valsa mali Migable et Yamada in solid culture systems. Liquid culture tests showed that the extracts at 800 mg/L inhibited mycelium dry weight by 96.5%. The synthesis of protein and glucose was inhibited to 45.2% and 23.0% of the control, respectively. Activities of chitinase and β-1,3-glucanase was 3.36 and 7.98 times higher than those of control, favorable to suppression of pathogenic fungi.