Essential oils and ethanolic extracts of lemongrass (Cymbopgon citratus), thyme (Thymus vulgaris) and marjoram (Origanum marjorana ) were screened for their possible antioxidant and antimicrobial properties as well as their chemical compositions. According to gas chromatography (GC/ MS) were identified, 39, 16 and 54 compounds of essential oils lemongrass, thyme and marjoram, respectively. The major constituents were 9-cisretinal , δ-2-carene and isomethyl-α-ionol for lemongrass; carvacrol, 2,5-dihydroxybenzoic acid and α –pinene for thyme and 9-cis-retinal, t-butylhydroquinone and p-mentha-3,8-diene for marjoram. The major phenolic and flavonoid compounds of ethanolic extracts identified using HPLC were benzoic , coumarin , hisperidin and hispertins for lemongrass; salicylic ,ellagic , hisperidin and rosmarinic for thyme and benzoic, pyrogalol, , hisperidin and narerigin for marjoram. Antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging. Results showed the superior of ethanolic extracts (low IC50) at lower concentrations than essential oils for scavenged DPPH. The antimicrobial activity (by disc diffusion tests) of different plant essential oils and extracts against 11 strains of microorganisms was done. The essential oils of the tested plants have a stronger antimicrobial activity than those of ethanolic extracts which did not exhibit antimicrobial activity against some microbial strains.