Abstract Investigation on the chemical constituents of EtOH extract of the Formosan soft coral Sinularia grandilobata, collected off the Kenting coast, has led to the isolation of six cembrane-type diterpenoids, grandilobatins A-F (1-6), and four steroids, sinugrandisterols A-D (7-10). All metabolites 1-10 are new natural products. The structures of 1-10 were elucidated by the analysis of spectroscopic data (MS, IR, 1D and 2D NMR) and by comparison of the related spectral data with those of related metabolites in literatures. The cytotoxicity assays of compounds 1-10 against the growth of cell lines, including MDA-MB-231(human breast cancer cell), MCF 7 (human breast cancer cell), Hep G2 (human liver carcinoma), and A-549 (human lung carcinoma), were carried out. The result showed that compound 5 exhibited moderate cytotoxicity against MDA-MB-231 cells. Compounds 7 and 8 showed moderate cytotoxicity against Hep G2 and MDA-MB-231 tumor cells and exhibited weak cytotoxicity against A-549 and MCF 7 tumor cells. Compound 9 showed weak cytotoxicity against A-549 and MCF 7 tumor cells.