A new source for 2S*,11S*,12R*-isosarcophytoxide (1), along with six known metabolites; 7R,8S-dihydroxydeepoxy-ent-sarcophine (2), sarcophytolol (3), sarcotrocheliol acetate (4), ent-sarcophine (5), guaiacophine (6) and gorgosten-5(E)-3I?-ol (7), was identified as Sarcophyton glaucum. The chemical structures were determined based on spectroscopic measurements (NMR, UV, IR and MS). The total extract and isolated compounds were evaluated against four cancer cell lines; HCT116 (human colorectal cancer), HT29 (human colon cancer), CACO-2 (colonic adenocarcinoma) and HepG-2 (human hepatocarcinoma). All tested compounds exhibited cytotoxicity against two cancer cell lines with IC50 in range 8.9ai??i??500 Ai??mol/L. Compounds (3) and (4) had significant cytotoxic effects towards HCT116, IC50 = 8.9 Ai?? 0.092 Ai??mol/L and 17.5 Ai?? 0.0.067 Ai??mol/L, respectively and against HepG-2, IC50 20.0 Ai?? 0.032 Ai??mol/L and 19.9 Ai?? 0.062 Ai??mol/L, respectively. The antiproliferative activities of compounds (3) and (4) can be attributed, at least partly, to their ability to induce cell cycle arrest, particularly in G0/G1 and S phases.