The objective of this study was to determine the in vitro resistance rates to 8 antibiotics of Escherichia coli isolated from cows with cases of clinical mastitis in Burdur province of Turkey during the 2000 to 2005 period. Antimicrobial susceptibility testing was performed on a total of 101 E. coli isolates. Only 9 of the isolates were susceptible to all tested antibiotics, while the remaining 92 isolates were determined to be phenotypically resistant at least to one of the antibiotics. Among the 8 antimicrobial agents tested, resistance was most frequent for trimethoprim/sulphamethoxazole, neomycin, oxytetracycline and gentamicin. The resistance rates of the isolates to enrofloxacin, danofloxacin, amoxycillin/clavulanic acid, cefuroxime, gentamicin, oxytetracycline neomycin and trimethoprim/sulphamethoxazole were 10.9%, 11.9%, 25.7%, 26.7%, 33.7%, 51.5%, 55.4% and 64.4%, respectively. In conclusion, the differences observed in the efficacy of the antibiotics tested to E. coli isolates indicate the importance of antibiotic susceptibility tests and periodic surveillance of the antibiotic susceptibilities of pathogenic bacteria.