A new cubitane-based diterpenoid, triangulene C (1), was isolated from the soft coral Sinularia triangula and its structure was elucidated on the basis of spectroscopic data. Compound 1 was not cytotoxic (IC50 > 20 microg/mL) toward the four human cancer cell lines tested (HL60, MDA-MB-231, HCT-116 and DLD-1).