A new dihydroagarofuran-based sesquiterpene, 15-acetoxyorbiculin A, was isolated from the root of Microtropis japonica, together with 13 known compounds. Their structures were determined through in-depth spectroscopic and mass-spectrometric analyses. Among the isolated compounds, celahin C and salasol A exhibited potent in vitro antituberculosis activity, both with an MIC value of 15.0 microg/ml against Mycobacterium tuberculosis H(37)Rv.