Mesembryanthemum nodiflorum L. (Aizoaceae) has long been used as food and in traditional medicine. This study was intended to explore the active groups within M. nodiflorum ethanolic extract and to study the cytological effects of M.nodiflorum water extract on Allium cepa L. root tips. Phytochemical analysis of M.nodiflorum ethanolic extract indicated the presence of alkaloids and triterpenes. Tannins, flavonoids and saponins did not found in M.nodiflorum alcoholic extract. Mitotic indices and distribution of cells in mitotic phases of A.cepa root tips were clearly changed after treatment with three different concentration of M.nodiflorum water extract (0.1, 1 and 3%) for 3h, 6h, and 12h. The maximum value of mitotic index 2.68% was observed after treatment with 3% for 6h, while the minimum value 1.35% was scored after 12h exposure to the same concentration. Different types of chromosomal aberrations were noticed. The present study revealed that M.nodiflorum water extract has a potent inhibitory effect on the mitotic activity of A.cepa root tip cells.