A new holostane-based triterpene glycoside, arguside A (1), was isolated from the sea cucumber Bohadschia argus, collected in the South China Sea. The structure of the new compound was elucidated by spectroscopic and mass-spectrometric analyses, in combination with chemical transformations. Compound 1 exhibited significant cytotoxicity against different human tumor cell lines, being more active towards HCT-116 cells (IC50 = 0.14 microM) than 10-hydroxycamptothecin (HCP) used as positive control.