Abstract:In order to study the toxicological effects of quaternary ammonium cationic surfactant to Botrytis cinerea, the toxicity morphology of conidia germination and cell wall were observed with microscope and scanning electronic microscope. The effect of quaternary ammonium cationic surfactant on the respiration of mycelial and conidia and the activity of cell wall degrading enzyme of B.cinerea were tested with the oxygen electrode method and UV-VIS spectrophotometry method. The activity of B.cinerea on tomato live leaves was observed with inoculating pathogens which were treated with quaternary ammonium cationic surfactant. The results indicated that the conidia germ tubes became short, wide and expanded. And the activity of polymethylgalacturonase, polygalacturonase and cellulose was obviously inhibited as well as the infection of B.cinerea on live leaves at the treatment of 5 μg/mL. After being treated with quaternary ammonium cationic surfactant at the concentration of 40 μg/mL, many different ventages emerged in the surface of cell wall and the intracellular materials gathered. The respiration of conidia was inhibited ob-viously at the dose of 100 μg/mL and the respiration of mycelia was destroyed obviously at 250 μg/mL and 1 000 μg/mL. In conclusion, the quaternary ammonium cationic surfactant can destroy the cell wall of B.cinerea and make it death at high doses. Furthermore they can also inhibit the activity of cell wall degrading enzyme and decrease the pathogenicity of B.cinerea at a low dose.