Urinary tract infection ( UTI) is a common disease , which may occur as Asymptomatic in both sexes at any age. Asymptomatic bacteriuria in pregnant women can particularly cause problems for both mother and her fetus. Therefore in this study 950 pregnant women who have been referred to Tabriz university and private, gynaecology clinics for routine pregnancy cares, and had no sign s of UTI were selected according to simple random sampling method. Their clean catch midstream urine were tested for 10 CFU/ ml). E. Coli proved to be the most prevalent organism (85℅) causing Asymptomatic bacteriuria in our patients. Other bacteria isolated were as follows: staphylococcus saprophyticus (5℅), Proteus mirabilia (4℅), streptococcus app.(2℅), klebsiella spp (2℅) , staphylococcus aureus(1℅) and enterobacter aerogenes(1℅). When antibiotic sensitivity patterns were performed according to Kirby_ Bauer method on our E. Coli strains the following sensitivity patterns were observed: amikacin(100℅), nalidixic acid(94.6℅), nitrofurantoin(90℅). Sensitivity of other isolated organisms are also discussed in detail. Results of our study indicate the presence of Asymptomatic UTI (10.5℅) in the pregnant women studies in Tabriz and underlined the need for recognition and treatment of them to prevent further problems in both pregnant women and their fetus.