Abstract Fractionation of the chloroformic extracts from Teucrium ramosissimum leaves resulted in the isolation of three flavonoids: genkwanin ( 1), cirsimaritin ( 2) and 4′,7-dimethoxy apigenin ( 4) and one sesquiterpene: β-eudesmol ( 3). The structures were determined using data obtained from 1H and 13C NMR spectra, as well as by various correlation experiments (COSY, HMQC and HMBC). The antioxidant activities of the isolated flavonoids from T. ramosissimum leaves were evaluated by measuring their ability to scavenge the radical ABTS + and through chemical assays: cupric reducing antioxidant capacity (CUPRAC), reducing power (RP) and ferric reducing antioxidant power (FRAP). Furthermore, the effects of T. ramosissimum isolated molecules, on inhibition of cell proliferation and induction of apoptosis in human leukemia cells, were also examined. Cirsimaritin showed the best activity in the ABTS assay with TEAC value 2.04 μM, whereas apigenin and 4′,7-dimethoxy apigenin exhibited the highest antioxidant activity using the CUPRAC, RP and FRAP assays with TEAC values 10.5, 1.39 and 0.71 μM respectively. The cytotoxic activity revealed that the β-eudesmol inhibited significantly the proliferation of K562 cells (IC 50 = 20 μg/ml).