The article will help Clinicians in predicting and planning correct strategies for UTI therapy.Backgrounds: Urinary Tract Infection (UTI) is one of the most common bacterial diseases worldwidethat can be presented asymptomatic or symptomatic, characterized by a wide range of symptoms from mild irritative voiding to bacteremia, sepsis, or even death. In latter decades, widespread utilization of antibiotics has resulted in increased incidence of antibiotic resistance among urinary tract pathogens all over the world. Objectives: The aim of this study was to determine patterns of antibiotic resistance bacteria isolated from urinary tract infections in the city of Karaj, Iran. Materials and Methods: This descriptive study was conducted in the city of Karaj from November 2009 to August 2010. Bacterial isolates were identified by standard biochemical tests. Antibacterial susceptibility test was performed by Kirby-Bauer method against some common antibiotics for Gram negative and Gram positive bacteria and the data were analyzed by SPSS software, version 12.0.1. Results: In this study, 230 (8.06%)out of 2852 patients showed positive urine cultures of which there were 204 (88.69%) females and 26 (11.3%) males. 180 (83.17%) cases of isolated bacteria were Gram negative bacilli while 50 (21.73%) cases were Gram positive cocci. E. coli isolates, as the most frequent Gram negative bacteria, showed high resistance to cephalothin (88.16%) and high susceptibility to nitrofurantoin (90.78%). Also Staphylococcus saprophyticus isolates, as the most frequent Gram positive bacteria, exhibited high resistance to ampicillin, tetracycline, and erythromycin (92.31%) and high susceptibility to nitrofurantoin and vancomycin (92.3%). Conclusions: considering the results of this study, E.coli isolates were the predominant pathogens in UTI. Our data demonstrated that antibiotics with the highest activity included ciprofloxacin and nitrofurantoin and those with the least activity included ampicillin and sulfamethoxazole-trimethoprim. Our findings reinforce the need for ongoing investigations to show the trends of antibiotic resistance which can help antibiotic prescription in the clinics.