Abstract:The volatile oil was obtained with steam distillation from Johnsongrass Sorghum halepense (L.) Pers. leaves. The chemical components were analyzed by the means of GC and GC-MS, and its biological effects on crops, weeds and microbial populations were studied. Twenty-six chemicals, 76.51% of total content, were isolated and identified from the volatile oil. The main component was sesquiterpenes, such as trans-α-berg-amotene (21.95%), α-patchoulene (10.77%), α-himachalene (4.66%), etc. Weed germination, crop shoot height and dry weight were significantly inhibited by the volatile oil. The volatile oil also significantly reduced the population of fungi and actinomycetes in the test soils, but significantly increased the population of bacteria in the soils. The results indicated that the volatile oil from Sorghum halepense demonstrated significant allelopathic potential on depressing surrounding plants and affecting microbial populations.