In the present study, two new trinor-guaiane sesquiterpenes, named clavuridins B (1), and A (2), along with three known sesquiterpenes (3-5), were isolated from the Xisha soft coral Clavularia viridis. Their structures and absolute configurations were determined on the basis of spectroscopic analysis, X-ray diffraction analysis with Cu Kα radiation and by comparison with related model compounds. Compounds 1 and 3-5 were evaluated for their cytotoxic activity.