Abstract: Streptomyces  can produce an overwhelming majority of known antibiotics and several biologically active compounds, but whether Streptomyces can display allelopathic effects on higher plants is largely unknown. In this study, seven actinomyces strains isolated from soils showed inhibitory effect on plant seedlings growth, among which, Streptomyces sp. 6803 had strong capability in inhibiting the seedlings growth of Brassica campestris and Echinochloa crusgalli in both solid and liquid cultures. The dilute solution (×5) of fermented broth inhibited the seedlings growth of B. campestris and E. crusgalli by 60.7% and 61.3%, respectively. Based on the morphological and physiologicalbiochemical characteristics and 16S rRNA sequencing, Streptomyces sp. 6803 was identified as Streptomyces arenae, with the 16S rRNA sequence identity being 99.28%. Ultraviolet radiation and diethyl sulfate (DES) were used to produce mutants to enhance the allelopathic potential of this strain. After 80 and 100 seconds of ultraviolet radiation, the dilute solution (×10) of fermented broth of obtained mutants UV8024 and UV100-2 showed 37.5% and 38.1% higher inhibition effect on the root growth of B.campestris seedlings, respectively,  compared with  the control. The mutant D507 obtained through 1% DES treatment for 50 min showed 29.8% higher inhibition effect on the root growth of B. campestris seedlings. This study showed that Streptomyces sp. 6803 had allelopathic effect on higher plants, and it was possible to enhance the allelopathic potential of the strain via mutation breeding.