the aim of the present study was the evaluation of the phytotoxic effect of essential oils (eos) from two labiatae species, namely thymus fontanesii boiss. et reut. and satureja calamintha subsp. nepeta briq. on some of the most harmful weeds in algeria (sinapis arvensis l., avena fatua l., sonchus oleraceus l., xanthium strumarium l. and cyperus rotundus l.). eos isolated by hydrodistilation were analyzed by gas chromatography-flame ionization detector (gc-fid) and gc-mass spectrometry (ms). carvacrol (52.1%), thymol (13.3%), p-cymene (12.2%) and -terpinene (8.1%) were the dominant compounds in t. fontanesii eo, while 1,8-cineole (28.4%), pulegone (10.2%), menthone (9.7%) and isomenthone (9.6%) were the most important constituents of s. calamintha eo. the bio-assessments showed a wide herbicidal effect on seed germination (eos at 0.01, 0.02 and 0.03%) and 3-4 leaf stage weeds (eos at 1, 2 and 3%) due to the disruption of their physiological process. based on our results, it can be concluded that the eos could be exploited for weed biocontrol.