The aim of present study was to determine the prevalence of O serogroups of Escherichia coli (E. coli) strains that cause community-acquired urinary tract infections (UTI) in children. In this study, 96 children with UTI referred to two Jahrom University-affiliated Hospitals in Iran were enrolled, during the period from August 2005 to August 2006. Drug sensitivity was tested by disk diffusion method and serotyping done by slide agglutination method. A total of 96 E. coli strains were isolated from urine samples of the study children whose age ranged from one month to 14 years. Cystitis was diagnosed in 49.2% and pyelonephritis in 50.8% of the study patients. Maximum drug resistance was seen with ampicillin (80.2%) and the least with imipenem (1.1%). The most common type of O antigen was O1 (12.2%). There was significant correlation between the presence of O antigens and sensitivity to nalidixic acid and gentamicin (P < 0.05). This is the first report of E. coli serotyping in children with UTI from the south of Iran and their relation to antibiotic resistance and clinical presentation. Further studies from other parts of Iran and on other serotypes are recommended.