Yuexiandajisu D, a novel 18-nor-rosane-type dimeric diterpenoid, was isolated from the roots of Euphorbia ebracteolata Hayata. Its structure was elucidated as 6,3':7,2'-diepoxy-di-2,3-dihydroxy-18-nor-ros-1(10),2,4,15-tetraene by spectroscopic techniques (HSQC, HMBC, DQF-COSY, TOCSY, NOESY) and chemical methods. Yuexiandajisu D showed moderate cytotoxic activity against cancer cell lines on HCT-8 and Bel-7402, with IC50 values of 2.66 and 3.76 μM, respectively.