[Objective]To study the diversity and bioactivity of endophytic actinomycetes isolated from mangrove plants collected in Macao and find the resources of medicinal microorganisms.[Methods]Twelve plant tissue samples collected at Lu Dang Cheng Mangrove Nature Reserve in Macao were grinded into powder after surface sterilization,and then spread on ten kinds of isolation media.Studies on diversity of actinobacteria in genus level were based on 16S rRNA gene sequence analysis,through with the alignment in the gene database.The antimicrobial activity of crude extracts from the fermentation broths were preliminarily tested against pathogenic microorganisms by disk diffusion method.Positive strains were preliminarily screened for PKSI、 PKSII and NPRS genes.[Results]216 actinobacterial strains were purified from these plant tissue samples.By comparison of 16S rRNA gene sequence,these strains were distributed in 34 different genus,which the dominant genus was Streptomyces.Antimicrobial preliminary test showed that 71 out of 85 fermentation strains exhibited positive results in at least one antifungal or antibacterial assay,and the total positive rate was 83.53%.63 of 71 strains with antimicrobial activity had at least one antibiotic biosynthetic gene including PKSI、 PKSII and NPRS genes,and 10 strains have all the three kinds of biosynthetic genes of antibiotics.[Conclusion]This study demonstrates that an unexpected diversity of actinobacteria colonizes inside the mangrove tissues,and these endophytic actinobacteria are promising sources for new secondary metabolites with bioactivity activities,which are waiting to be explored.