Abstract: ObjectiveThe diversity of actinomycetes isolated from bottom mud of mangrove forest in Beilun Estuary of Guangxi and the antibacterial activity of its secondary metabolites against Sporisorium scitamineum were studied in or-der to lay a foundation for finding new actinomycetes species and the corresponding agricultural fungicides.MethodSamples from bottom mud of mangrove forest in Beilun Estuary of Guangxi were isolated and cultured with the method di-lution coating in six isolation media.Strains were purified with the culture medium ISP2.Diversity of actinomycetes was analyzed by 16S rRNA gene sequencing.The antibacterial activity of isolated strain against S.scitamineum were initially tested with the method of Oxford cup.ResultThere were 36 strains were isolated from bottom mud of mangrove forest in Beilun Estuary of Guangxi through removal of duplication,combination,and comparison of 16S rRNA gene sequence. The strains distributed in 12 genera,9 families and 6 orders;Streptomyces was dominant genus.The similarity of 16S rRNA gene sequences between the five strains and standard strain was bleow 98.00%.The result indicated the five strains were potential new species.The test result of antibacterial activity showed that among 36 actinomycetes strains,22 strains had antibacterial effectson S.scitamineum,accounting for 61.11% of total isolated actinomycetes.ConclusionThe bo-ttom mud of mangrove forest in Beilun Estuary of Guangxi is abundant with marine actinomycetes resources,which pro-vides potential for development of new agricultural fungicides.