Abstract: The aim of this study is the evaluation of the synergistic effect of sub-MIC doses of ciprofloxacin with water soluble green tea extract against urinary tract isolates of E. coli. A total of 18 isolates were collected from urine specimens submitted to a clinical diagnostic Laboratory in Urmia, Iran. The amounts of MIC and MBC for green tea water extract, ciprofloxacin or a mixture of green tea with sub-MIC doses of ciprofloxacin were determined and three groups were compared. The Synergism between ciprofloxacin and water soluble green tea extracts were seen for 93.7% (15 of 16 tested) of bacterial isolates. This study suggests that combination of water soluble green tea extracts and ciprofloxacin has in vitro synergistic effect on urinary tract isolated E. coli.