A new macrolactone glycoside, lecythomycin (1), 23-methyl-3-(1-O-mannosyl)-oxacyclotetracosan-1-one, was isolated from the endophytic fungus Lecythophora sp. (code 30.1), an endopyte of the Indonesian plant Alyxia reinwardtii. The structure of 1 was elucidated on the basis of NMR spectroscopic and mass spectrometric data. The isolated compound displayed antifungal activity against strains of Aspergillus fumigatus and Candida kruzei at minimal inhibitory concentrations (MIC) of 62.5-125 microg/mL.