[Objective] To study the diversity and bioactivity of actinobacteria isolated from Mangroves in Dongzhaigang, Hainan. [Methods] Various tissues from 14 kinds of mangrove plants as samples were collected from Dongzhaigang National Nature Reserve in Hainan, China. Samples were grinded into powders after surface sterilization and cultured on 10 different media for strain isolation. To determine the phylogenetic position of the strains, 16S rRNA gene sequences were obtained by PCR amplification and direct sequencing, then compared with gene database. The antifungal and antibacterial activities of the crude extracts were tested by disk diffusion method. Screening of PKS I, PKS II and NRPS genes was carried out by PCR and agarose electrophoresis. [Results] 146 strains affiliated to 18 genera were obtained. The dominant genus is Streptomyces. The highest similarity of 16S rRNA gene sequence between strain S3Cf-2 and the validly described species Couchioplanes caeruleus DSM44103T, between strain S3Af-1 and the validly described species Microlunatus terrae BS6T was 97.45% and 97.43%, respectively, which indicated that the strains S3Cf-2 and S3Af-1 were potential new taxa. The antimicrobial activity of crude extracts from the fermentation broths were tested against different pathogenic microorganisms by paper-disc diffusion method. Antimicrobial test showed that 40 out of 46 strains exhibited positive results in at least one antifungal or antibacterial assay, and the total positive rate was 86.96%. Thirty eight in 40 strains with antimicrobial activity, probably, had at least one antibiotic biosynthetic gene including NRPS, PKS I and PKS II, and 14 strains have all the three kinds of biosynthetic genes of antibiotics. [Conclusion] The study demonstrates that diversity of endophytic actinobacteria from mangrove are rich and mangrove tissues as a special niche for discovery of new pharmaceutical microorganisms are waiting to be explored.