Four new diterpenoids, pachyclavulariaenones D-G (1-4), have been isolated from the soft coral Pachyclavularia violacea. The structures and relative stereochemistry of metabolites 1-4 were established on the basis of extensive NMR studies and chemical methods. The structure, including the relative configuration of pachyclavulariaenone F (3), was further confirmed by a single-crystal X-ray analysis. Pachyclavulariaenone G (4) has been shown to exhibit significant cytotoxicity toward P-388 and HT-29 cancer cells.