Abstract: An isolate strain of Bacillus subtilis was found in pomegranate fruit,and a preliminary study on the inhibitory effect of the volatile substances produced by B.subtilis against several common trees and fruits diseases was carried out.The results showed that the growth of mycelia were inhibited by the volatile substances,and the bacterstatic ratio for Botryosphaeria dothidea can reach 60%.Compared to normal mycelia,different pathogens showed different changes after treatment by the volatile substances for B.dothidea and Coniothyrium diplodiella,the mycelial branches were increased and distorted,and the top area and middle cell of mycelia became intumescentia.For Valsa sordida and Helicobasidium purpureum,the mycelia were stubbed;for Fusarium oxysporum,the mycelia became much slimmer;however the mycelia of T.roseum were not changed significantly.The speed of pigment production of mycelia were also inhibited by the volatile substances.The results suggested that the volatile substances had different bacteriostatic actions on different pathogens.