The aim of the research was to elucidate the antitumor bioactive compounds from soft coral Sinularia sp. Sinularia sp. were taken from Buna ken Island waters in Manado Indonesia. The area is well known for its high marine biota diversity. Elucidation of the active fraction was conducted by using C18 Column Chromatography followed by Preparative High-Pressure Chromatography (HPLC). The masses data of the compound was determined by Liquid Chromatography Mass spectrometer (LCMS) Method and Fourier Transfer Mass Spectrometer (FT-MS). Structural elucidation was done by using Spectrometer Resonance Magnetic Nucleoid (NMR) (Joel Resonance) Method. Toxicity test was conducted on cancer cell line of Hela, T47D and MCF7 using 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT test) method. The result of toxicity test of bioactive compound from Sinularia sp. are one new compound. The new compound, the IC50 is 0.64 mg/l for HeLa cells, 12.1 mg/l untuk T47D cells and 1.02 mg/l for MCF-7 with a molecular formula of C20H28O5; exact mass 348.19 [M+NH4]+365.132. Data for the result shows that the new compounds have biological activities toward cancer cells.