Investigations on the cytotoxic effects of the crude methanol and fractionated extracts (hexane, ethyl acetate) C. mangga against six human cancer cell lines, namely the hormone-dependent breast cell line (MCF-7), nasopharyngeal epidermoid cell line (KB), lung cell line (A549), cervical cell line (Ca Ski), colon cell lines (HCT 116 and HT-29), and one non-cancer human fibroblast cell line (MRC-5) were conducted using an in-vitro neutral red cytotoxicity assay. The crude methanol and fractionated extracts (hexane and ethyl acetate) displayed good cytotoxic effects against MCF-7, KB, A549, Ca Ski and HT-29 cell lines, but exerted no damage on the MRC-5 line. Chemical investigation from the hexane and ethyl acetate fractions resulted in the isolation of seven pure compounds, namely (E)-labda-8(17),12-dien-15,16-dial (1), (E)-15,16-bisnor-labda-8(17),11-dien-13-on (2), zerumin A (3), β-sitosterol, curcumin, demethoxycurcumin and bis-demethoxycurcumin. Compounds 1 and 3 exhibited high cytotoxic effects against all six selected cancer cell lines, while compounds 2 showed no anti-proliferative activity on the tested cell lines. Compound 1 also demonstrated strong cytotoxicity against the normal cell line MRC-5. This paper reports for the first time the cytotoxic activities of C. mangga extracts on KB, A549, Ca Ski, HT-29 and MRC-5, and the occurrence of compound 2 and 3 in C. mangga.