A new phenanthraquinone, 7,9-dihydroxy-2-methoxy-1,4-phenanthraquinone (1), and nine known compounds were isolated and identified from the whole plants of Dendrobium lindleyi. The structure of the new compound was determined on the basis of NMR (1D and 2D) and mass spectroscopic analysis. The new compound exhibited potent antimicrobial activity against Bacillus subtilis and Escherichia coli, and its activity was comparable with that of the well-known antibacterial drug berberine.