Abstract: In order to study the inhibitory effect of Hypocrellin A(HA) on Botrytis cinerea, the inhibition rate, conductivity, leakage of protein and nucleic acid, mycelial morphology and ultrastructure of B.cinerea that being treated with HA were determined by methods of mycelium growth rate, conductivity, UV spectrophotometry and electron microscope, respectively. The results showed that HA had weak or even no antifungal activity to B. cinerea in the dark; but under luminous intensity of 12 000 lx, the activity was obvious, with an EC50 value of 17.16 mg/L, and the inhibition rate increased significantly with the increase of HA concentration, the inhibition rate could reach 73.9% at 40 mg/L HA; The conductivity, leakage of protein and nucleic acid rose obviously as the concentration of HA increased. According to the results of electron microscope, most of hyphae malformed with swollen or constriction after being treated by 34.32 mg/L HA; Meanwhile, almost all the organelles disappeared and cavities with large area appeared in the cells, suggesting the cells were damaged severely. The results of present study provided theoretical basis for developing HA as a novel green biological pesticide.