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The concept of biological control for health maintenance has received widespread attention during the last few years. Therefore, the main objective of this work was to look for active substances that couldbe used as antimicrobial agents in an efficient and safe manner. To achieve this target, five different extracts (ethyl acetate, chloroform, diethyl ether, methanol and water) from three blue green algalspecies (Anabaena flos aquae (Linnaeus) Bory; Anabaena variabilis (Kützing) and Oscillatoria angustissima West and West) were examined. This different algal extracts were tested in vitro for their antimicrobial effects against eight Gram +ve and Gram -ve bacteria in addition to two groups of fungi (filamentous fungi and yeast) using agar well diffusion method. The results showed that the ethyl acetate extract of A. flos aquae notably inhibited nearly the whole tested bacteria and filamentous fungiwith minimal activity against tested yeasts. Furthermore, a significant reduction in sporulation as well as dry weight of the two filamentous fungi was found with ethyl acetate extracts. The toxicity of ethyl acetate extract to Artemia salina showed that the effective concentration that would inhibit their growth by 50% (LC50) after 24 h of incubation was 17, 41 and 45 mg.ml-1 for A. flos aquae, A. variabilis and O. angustissima, respectively. The antagonistic materials from ethyl acetate extract of differentcyanobacterial species were identified using gas liquid chromatography mass spectrometer (GC-MS). The main components of ethyl acetate extract of A. flos aquae consisted of heptadecane and 7-methylheptadecane representing 26.11 and 18.65%, respectively.