Five HIV-RTase inhibitors, macrocarpals A-E, have been isolated from Eucalyptus globulus. X-ray diffraction studies as well as spectral and chemical investigations established the structures 1, 2, 3, 12, and 13, respectively. A large number of terpenoids, phloroglucinols, and their coupled compounds have been isolated and characterized from a variety of Eucalyptus plants, and some of these exhibit interesting biological activities. We found ethanol extracts of leaves and calyces of E. globulus show significant inhibitory activity of HIV-RTase. Fractionation of the active principles afforded five sesquiterpene-isopentyl phloroglucinol coupled compounds. Although one of them has been already reported by the name of macrocarpal A (1), we wish to describe herein the structures of new macrocarpals. Determination of the absolute structures of macrocarpals A (1) and C (3) based upon modified MTPA method are also described.