Abstract：The macromolecular substances larger than 14 kD in weight， secreted by Botryis cinerea were extracted with dialysis method. These substances were directly inoculated into the leaf blades of tomato and chrysanthemum to detect their phytotoxicity. And the laccase property of these Botryis cinerea secreta was identified using tannic acid and RB light blue as the indicator. The results showed that the extracellular macromolecule substances secreted by B. cinerea could lead to leaf tissue necrosis， suggesting that they were toxic to the plants. The results also showed that 3 days after inoculation of B. cinerea， there appeared chromogenic reaction on tannic acid and RB light blue plate. And 6 days later， the plate’s color changed almost completely，indicating that the extracellular macromolecule substance had the properties of laccase.