In vitro biological activities including anti-phytopathogenic fungi, antibacterial, antifeedant and herbicidal activities of the extracts from the heartwoods of Mansonia gagei Drumm. were evaluated. The dichloromethane(DCM) extract displayed antifungal activity against four plant pathogenic fungi(Alternaria porri, Colletotrichum gloeosporioides, Fusarium oxysporum and Phytophthora parasitica) higher than the methanolic(Me OH) extract. The separation of the DCM extract using bioassay guided antifungal activity against P. parasitica led to the isolation of mansorins A, B, and C, mansonones C, E, G and H. Among isolated compounds, mansonone E displayed the highest antifungal activity against P. parasitica, followed by mansonone C, mansorin B and mansonone G. This potent compound revealed the same minimum inhibitory concentrations(MIC) of 31 μg mL~(–1) against C. gloeosporioides and P. parasitica, and minimum fungicidal concentration(MFC) of 31 and 125 μg mL~(–1), respectively. Moreover, mansonone E exhibited highly significant antibacterial activity against both Xanthomonas oryzae pv. oryzae(Xoo) and X. oryzae pv. oryzicola(Xoc) with MIC and minimum bactericidal concentration(MBC) as 7.8 and >500 μg mL~(–1), respectively. This compound furthermore could inhibit the feed of Spodoptera litura with 45.9% antifeedant and significantly herbicidal activity reduced the shoot and root growth of Brassica chinensis, Oryza sativa, Mimosa pigra and Echinochlooa crus-galli. Mansonone E has potential as a new natural pesticide for agricultural plant pathogen management. The vitro (DC) extract antifungal activity against four plant pathogenic fungi (Alternaria porri, Colletotrichum gloeosporioides , Fusarium oxysporum and Phytophthora parasitica) higher than the methanolic (Me OH) extract. The separation of the DCM extract using bioassay guided antifungal activity against P. parasitica led to the isolation of mansorins A, B, and C, mansonones C, E, G and H. Among isolated compounds, mansonone E displayed the highest antifungal activity against P. parasitica, followed by mansonone C, mansorin B and mansonone G. This potent compound revealed the same minimum inhibitory concentrations (MIC) of 31 μg mL ~ (- 1) against C. gloeosporioides and P. parasitica, and minimum fungicidal concentration (MFC) of 31 and 125 μg mL -1, respectively. Moreo ver, mansonone E extraction highly significant antibacterial activity against both Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc) with MIC and minimum bactericidal concentration (MBC) as 7.8 and> 500 μg mL -1 , respectively. This compound to could inhibit the feed of Spodoptera litura with 45.9% antifeedant and significantly herbicidal activity reduced the shoot and root growth of Brassica chinensis, Oryza sativa, Mimosa pigra and Echinochloa crus-galli. Mansonone E has potential as a new natural pesticide for agricultural plant pathogen management.