In order to search for bioactive compounds, we have studied the chemical constituents from the organic extracts of the soft coral Sarcophyton stellatum, collected from Dongsha Atoll. This study had led to the identification of sixteen natural diterpenoids, including six new compounds, stellatumonone (1), stellatumolides A¡VC (2¡V4) and stellatumonins A¡VB (5¡V6), along with ten known compounds. The structures of compounds 1¡V16 were established by detailed spectroscopic data (IR, MS, 1D, 2D NMR) and by comparison of the spectral data with those of the related known compounds. The cytotoxicity of compounds 1¡V16 against the HepG2 (human liver hepatocellular carninoma cells), MDA-MB231 (human breast cancer cells) and A549 (human respiratory epithelial cells) cancer cell lines were determined. Among them, compound 16 showed cytotoxic activity toward the A549 cancer cells.