Methanol extract from aerial parts of Sideritis libanotica Labill. subsp. linearis (Bentham) Borm. were investigated for its in vitro antiproliferative activities against Vero, HeLa and C6 cells. The tests were carried out as dose-dependent assay starting from 25 mu g/mL to 250 mu g/mL. The extract found to be active against African green monkey kidney (Vero), human uterus carcinoma (HeLa) and Rat Brain tumor cells (C6) cancer cell lines with IC(50) values. The methanol extract of S. libanotica showed the highest activity against the Vero, HeLa and C6 cell lines at 250 mu g/mL as dose-dependent assay starting from 25 mu g/mL.