Technical Abstract: Muscodor yucatanensis, a recently described endophytic fungus, was isolated from the leaves of Bursera simaruba. In the present study we tested in vitro the mixture of volatile organic compounds (VOCs) produced by M. yucatanensis for the allelochemical effects against phytopathogenic fungi and fungoids, other endophytic fungi, and plants. We also tested organic extracts of the mycelium and culture medium. VOCs were lethal to Alternaria solani,Rhizoctonia sp., Phythophthora capsici, P. parasitica, Guignardia manguifera, Colletotrichum sp., and Phomopsis sp., but had no effect on Fusarium oxysporum, Xylaria sp., and the endophytic isolate 120. VOCs didn’t have any self-inhibitory effect on the growth of M. yucatanensis, but they did exhibit phytotoxic activity causing inhibition of root length of amaranth, tomato, and barnyard grass, particularly in the first 15 days of growth of the fungus. The majority of VOCs were identified by gas chromatography/mass spectrometry. Almost all compounds identified in the VOCs mixture were not previously reported from other Muscodor species. Only four known compounds appeared in the VOCs mixture of M. yucatanensis: octane,1-butanol, 2-methyl-, acetate, furan, 2-pentyl-, caryophyllene and aromadendrene. We also investigated the effects of organic extracts of M. yucatanensis on the same phytopathogens, endophytes, and plants. In general, root length of plants was more inhibited than radial growth of phytopathogens and endophytic fungi. The culture medium extract produced more inhibition than the mycelium extract. We discuss the possible allelopathic role that the metabolites of M. yucatanensis play in its ecological interactions with its host plant and other organisms.