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【Objective】To provide a reference for finding eco-friendly antibacterial agents, the diversity of endophytic fungi in the medicinal plant Thespesia populnea in mangroves and their antifungal and antibacterial activities were studied. 【Method】Endophytic fungi were isolated and purified from the stem, leaf and bark tissues of the medicinal plant T. populnea in Guangxi Beibu Gulf mangroves, and identified by a combination of morphology and molecular biology. Colletotrichum from Diospyros kaki, Juglans regia, Litchi chinensis, and Fusarium oxysporum f. sp. cubense 1（FOC1), Fusarium oxysporum f. sp. cubense 4（FOC4), and Alternaria cucumerina from Cucumis sativus, as well as endophytic fungus Alternaria alternata from Avicennia marina, and Streptococcus iniae from Oreochromis niloticus, were selected as indicator organisms. The antifungal and antibacterial activities of endophytic fungal extracts were screened by plate confrontation method and filter paper method. 【Result】A total of 60 strains of endophytic fungi were isolated and purified from T. populnea, belonging to 5 genera and 25 species. Among them, the genera Colletotrichum and Diaporthe were dominant, with the isolation rates of 48. 33% and 26. 67%, respectively. The rest were Botryosphaeria, Didymella and Cryptosporella, with isolation rates of 15. 00%, 6. 70% and 3. 33% respectively. The most strains were isolated from the bark tissue of T. populnea, with a total of 4 genera and 23 strains, accounting for 38. 33% of the total isolation amount, followed by leaf tissue（31. 67%) and stem tissue（30. 00%). In addition, 12 endophytic fungi were found to have ITS rDNA sequence similarity of less than 95. 00% with NCBI database, indicating that they might be potential new species. The results of antifungal and antibacterial activities indicated that J1-20 had strong antifungal and antibacterial activities against the 8 selected indicator organisms. The antifungal rates against Colletotrichum of D. kaki, Colletotrichum of J. regia, Colletotrichum of L. chinensis, FOC1 and FOC4, A. cucumerina from C. sativus, A. alternata from A. marina, were 39. 39%, 25. 00%, 19. 10%, 32. 43%, 28. 20%, 89. 00% and 74. 19%, respectively. Meanwhile, the inhibitory zone of J1-20 against S. iniae was 21. 00 mm. 【Conclusion】The endophytic fungi in T. populnea have rich diversity and relatively uniform distribution. Among them, J1-20 has broad-spectrum antifungal and antibacterial activities against 8 indicator organisms and has good development potentials. [ABSTRACT FROM AUTHOR]