The Eulophia plants belong to the Orchidaceae family. There are 5 species reported to be found in Thailand1 and among which E. nuda has been studied and several phenanthrene derivatives isolated.2,3,4 Since there have been no report on the phytochemical study of E. graminea (Hua khaao tom, in Thai) and the extract of tubers of this plant was used as eardrop.5 We therefor aim to isolate the chemical constituents of E. graminea tubers and evaluate the antimicrobial activity of the pure compounds.