The antimicrobial activity of two Egyptian plants; Sisymbrium irio and Pteranthus dichotomus were studied against urinary tract infections (UTIs) bacteria. One hundred clinical material samples from urinary tract of patients were collected from Egyptian hospitals and laboratories. Different methods were used for the identification of the isolated bacteria: conventional biochemical methods, cultural characterization and Analytical Profile Index test (API 10S strep test systems). Eight gram-negative (G-ve) bacteria: Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, Proteus mirabilis, Acinetobacter baumannii and one gram-positive (G+ve) bacterium were isolated from patients with UTIs. The extracts of the two selected plants were tested for their effect against isolated bacteria. Sisymbrium irio extract greatly inhibited the growth of bacteria more than that of Pteranthus dichotomus. Successive extracts of Sisymbrium irio were prepared and their effects were studied against bacteria. The most effective extract was ethyl acetate extract. Three flavonoid compounds were isolated from it. Their activity was tested against isolated bacteria. The most active one was isolated and identified as apigenin-7-O-β-D-galactoside. Experimental infection of mice was done with three selected isolated bacteria that were sensitive to successive extracts (Enterococcus faecalis, Citrobacter freundii and Acinetobacter baumannii). In control positive group, bacteria remained in urine for more than five days. While treating mice with ethyl acetate extract, the bacteria decreased in the urine and disappeared and the number of pus cells was greatly decreased.