Abstract: The damage to Eupatorium adenophorum on different organs by toxin produced by brown spot needle blight fungus and the damage effect to the leaves of Eupatorium adenophorum by crude toxin extract of brown spot needle blight fungus with varied concentrations were studied. Bioassay methods was introduced to study the poisonous activity of the toxin to catalase of the callus and leaves of Eupatorium adenophorum by tissue culture. The results indicated that leaves of the weed were the most sensitive organ of the weed to the toxin, which could be significantly damaged by doubly diluted crude extract. The root was the least sensitive. Callus of Eupatorium adenophorum could differentiate and grow well in MS medium (with 6 mL of 2, 4- D 1 mg/mL). Treated by toxin, the CAT activity of leaves and callus of Eupatorium adenophorum could rise to the uppermost within 6 h and then declined.