Four new 2-benzoxazolinone-type alkaloids (acanthosides A-D) along with three known ones were isolated from the roots of Acanthus ilicifolius. Their structures were established by detailed interpretation of one dimensional (1D)- and two dimensional (2D)-NMR as well as high-resolution electrospray ionization (ESI)-MS data. The antiproliferative activities of these compounds were evaluated in vitro against three cultured cancer cell lines. The new compounds exhibited different levels of cytotoxicity against the HepG2, HeLa, and A-549 cancer cell lines with IC50 range 7.8-26.6 µM. In comparison with known compounds, the new isolates displayed better cytotoxic activities, which was attributable to the presence of substituted benzoyl moiety in their structures.