The present work was achieved to find the active chemical constituents and to evaluate the antimicrobial activity of some medicinal plant extracts on six pathogenic bacteria include ; Escherichia coli,  Salmonella sp., Shigella flexneri, Enterobacter sakazakii, Staphylococcus aureus and Bacillus cereus by agar well diffusion method. A qualitative phytochemical analysis was performed for the detection of alkaloids, saponins, terpenes, flavonoids, tannins and glycosides. The results revealed that Rosmarinus officinalis (rosemary), Citrus sinensis (orange peel), Eucalyptus globulus (camphor), Psidium guajava (guava), Matricaria chamomilla (chamomile), Allium cepa (onion), Allium sativum (garlic) and Nigella sativa (black seed) contain alkaloids, flavonoids, tannins, terpenes, saponins and glycosides. Also the plant extracts of bothrosemary, orange peel, camphor, guajava, showed highest significant effect against all tested pathogenic bacteria followed by chamomile, onion and garlic showed lowest significant effect but black seed showed no effect.  Salmonella sp. exhibited resistance to most plant extracts. This study revealed the presence of bioactive compounds in these plants which have antibacterial properties, can be useful as an alternative antimicrobial agent for treatment infectious diseases and in pharmaceutical industries.