The essential oils obtained from different officinal plants of Lebanon, belonging to the Magnoliophyta division, have been tested for their antiproliferative activity on human erythroleukemic K562 cells. Satureja montana showed the most interesting biological activity in inhibiting the cell growth and inducing erythroid differentiation of K562 cells. The essential oil of Satureja montana was therefore analyzed using a GC/MS (gas chromatography/mass spectrometry) system in order to identify the major constituents and compare them with analysis performed on Satureja hortensis. We demonstrated that the essential oil composition varied with the species, the major constituent of Satureja hortensis being carvacrol (50.61%) and that of Satureja montana being alpha-terpineol (12.66%). In order to identify molecules possibly responsible for the biological activity, commercially available derivatives have been assayed on the K562 cell line. Satureja montana essential oil displayed different natural derivatives characterized by higher activity than those present in Satureja hortensis. The common active principles are alpha-pinene, gamma-terpinene, 4-terpineol, alpha-terpineol, tau-cadinene, tau-cadinol and caryophyllene. Both caryophyllene and alpha-terpineol showed important antiproliferative effects on K562 cells.