A new dimeric sesquiterpene, dicarabrol (1), together with three known sesquiterpenes, carabrol (2), 11(13)-dehydroivaxillin (3), and 2-desoxy-4-epi-pulchellin (4), were isolated from the whole plant of Carpesium abrotanoides L. Their structures were elucidated on the basis of spectroscopic analysis, and single crystal X-ray diffraction analysis. Compound 1 possessed a dimeric sesquiterpene core featured with a cyclopentane ring connecting two sesquiterpene lactone units rarely discovered in nature. Dicarabrol (1), as well as three known sesquiterpenes (2-4), had potent in vitro cytotoxicities against the K562, MCF-7, Hela, DU145, U937, H1975, SGC-7901, A549, MOLT-4, and HL60 cell lines with IC50 values ranging from 0.10 to 46.7 μM, while they showed significant antiviral (H1N1 and H3N2) activities. Furthermore, compounds 1, 3 and 4 displayed significant antimycobacterial activity (IC50 3.7, 6.0, and 7.6 μM, respectively).