Background and Objectives: Urinary tract infection is one of the most common bacterial infections in the human population, and more frequent infection during pregnancy. With notice to this point that most of urinary tract infections during pregnancy are asymptomatic, they could lead to serious complications such as prematurity, low-birth weight, hypertension, and higher fetal mortality rates ifuntreated. This study was aimed to determine the prevalence of asymptomatic bacteriuria, bacterial agents and their antibiotic susceptibility pattern in pregnant womenattendingSemnan public health centers during 2007-8. Patients and Methods: In this descriptive cross sectional study,pregnant women attending Semnan public health centers during May 2007 and June 2008 were investigated. Clean catch mid stream urine samples were collected and cultured on Eosin Metylene Blue agar and Blood agar by calibrated loop method. Suspected colonies were identified, antibiotic susceptibility test was done. Results: Of 297 samples, 10 (3.3%) were positive for asymptomatic urinary tract infection. The dominant bacterial isolate was Escherichia coli (70%). The antibiotic susceptibility was observed to ciprofloxacin, ceftazidime and cefotaxime (80%), the most resistance was amoxicillin- clavulanic acid (90%). Conclusion: Frequency of asymptomatic UTI in pregnant women in this study is significantly lower than similar studies. Antibiotic susceptibility rate to using antibiotics do not show significant differences with most other studies.