A large number of plants have therapeutic potentials. Of these plants black cumin, Nigella sativa L. ( Ranunculaceae); onion, Allium cepa L.
( Alliaceae ) and leek , Allium porrum L. (Alliaceae ) were examined in this investigation in form of methanolic and aqueous extracts. Two different concentrations were prepared and examined for each plant extract. Eight microoraganisms were examined in this investigation. Two strains of Gram positive bacteria(G+) , Bacillus subtilis and Micrococcus luteus ; two strains of Gram negative bacteria(G-), Salmonella typhi and Eschrichia coli ; two strains of yeasts, Candida lipolytica and Saccharomyces cerevisae and two fungal strains, Aspergillus niger and Penicillium natatum. Results of chemical analyses proved that all methanolic extracts of three examined plants contained terpenes, flavonoids, saponins and alkaloids except the methanolic extract of  black cumin contained tannins . Furthermore, the extracts of the tested plants seeds were found to contain some minerals such as Zn,Fe,Mn,Na,K,Ca,Mg and P. Results of microbiological examination exhibited that methanolic extracts either in 0.05% or in 0.1% was more effective than the aqueous extract for all the tested microbial strains.