The objective of this study was to determine the in-vitro and in-vivo activity of cranberry extracts against Escherichia coli O157:H7. This strain of E. coli was the most common etiologic agent of urinary tract infections isolated from patients. Filter sterilized aqueous and methanol extract of cranberry was prepared and used in the present study. The aqueous extract of cranberry produced inhibition zone ranging from (10.8-23.8) mm against the tested bacteria. While the methanol extract produces larger zones of inhibition (12.1-24.2) mm against the bacteria. The minimum inhibitory concentration (MIC) for the methanol and aqueous extract was 0.35 and 0.625 mg/ml, respectively. In vivo study involved inducing UTI in rats and then treated with (200 mg/kg B.W) aqueous and methanol extract and compared with Gentamicin treatment at a dose of (2 mg/kg B.W) subcutaneously for 14 days. Methanol extract succeeded in treated UTI caused by Escherichia coli in the infected rats and prevented infection comparing with aqueous extract and Gentamicin. Food, water intake, body weight, pH and creatinine level returned to normal values after treatment with methanol extract of Cranberry fruit (200 mg/Kg.B.W) comparing with aqueous extract of Cranberry fruit and 2 mg/Kg.B.W. of Gentamicin. These parameters used in this current study as indicator for curing from infection. These findings indicated that cranberry extract was effective at all levels in inhibiting E. coli O157:H7; thus it possesses antimicrobial activity and hold great promise as an antimicrobial agent.