The purpose of this study was to investigate development of resistance to fluoroquinolones in Escherichia coli strains causing urinary tract infections. The ciprofloxacin, ofloxacin and levofloxacin susceptibility of E. coli strains isolated in 1999 and 2002 from the urine samples at the Bacteriology Laboratory, Microbiology and Clinical Microbiology Department, Faculty of Medicine, Celal Bayar University, were investigated by using microdilution method. Minimum inhibition concentration (MIC) ranges were determined as 0.03-128 µg/mL for ciprofloxacin and ofloxacin; 0.03-32 µg/mL for levofloxacin in the 40 E. coli strains isolated in 1999. Ciprofloxacin, ofloxacin and levofloxacin MIC50 values were 0.03 µg/mL, MIC90 values were 32 µg/mL for ciprofloxacin and ofloxacin, and 16 µg/mL for levofloxacin. The MIC ranges were found 0.03-128 µg/mL for ciprofloxacin and ofloxacin, and 0.03-64 µg/mL for levofloxacin in the E. coli strains isolated in 2002. MIC50 values were 0.03 µg/mL for all of the three antibiotics, MIC90 values were 128 µg/mL, 64 µg/mL and 32 µg/mL for ciprofloxacin, ofloxacin and levofloxacin, respectively. While the ciprofloxacin, ofloxacin and levofloxacin resistance rates in uropathogenic E. coli strains isolated in 1999 were found 30%, it was seen that those rates increased to 34% in the strains isolated in 2002. As a result, the susceptibility of uropathogenic E. coli strains to floroquinolones has gradually decreased. Thus, before deciding on the fluoroquinolone therapy, antibiotic susceptibilities of the pathogens causing urinary tract infections should be investigated and necessary precautions should be taken against resistance development.