Artemisia (Asteraceae family) has been reported to possess different bioactive phytochemicals including phenols, sesquiterpene lactones and flavonoids. The aim of this study was to estimate the anti-proliferative activity of the methanolic extract of Artemisia herba alba using in vitro assays on two of human cancer cell lines compared with the normal cell lines. The obtained results indicated that A.herba alba extract showed highly cytotoxic and anti-proliferative effects on tested human cancer cells as revealed by measuring viable mitochondrial oxidation of [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay] (MTT assay). The observed (-IC50-) or the half-maximal inhibitory concentration of A. herba alba extract in the human hepatocellular carcinoma (HepG2) was 50.34 μg/ml, while in the lung cancer cell line (A549) it was 29.23 μg/ml. In contrast, the normal liver cells (THLE2) as well as lung normal cells showed very low sensitivity toward tested extract where the IC50 were 1250μg/ml and 1915 μg/ml, respectively. However, flow cytometric analysis for cell cycle using propidium iodide staining revealed increment of G2/M phase cell cycle arrest after treatment of HepG2 cells with A. herba alba extract. At the molecular level, the quantitative real time-PCR technique was used to investigate the alteration of gene expression after exposure of HepG2 cell line to A. herba alba extract by measuring levels of mRNA for p53, Bax, and Bcl-2 genes expression. The apoptotic mechanism was activated by the crude extract of A. herba alba extract included up-regulation of p53 and Bax and downregulation of Bcl-2 expression levels. However, no cytotoxic effect was recorded after exposure of normal cell lines to the plant extract. These data indicated that A. herba alba extract possess antiproliferative effect by a cell cycle arrest at the G2/M phase and apoptosis mediated cytotoxicity in carcinoma cells. These results suggested that A.herba alba could contain one or more effective anti-cancer compound(s) and can be used as a natural source of anticancer agents.