The aim of this study was to evaluate in-vitro activity of Cefamandol and Ceftazidime, in combination with potassium clavulanate against 10 uropathogenic E.coli isolated from patients with chronic complicated urinary tract infections (UTIs), these isolates were identified by the Api identification systems.The antimicrobial susceptibility tests were determined by Kirby-Bauer method and the minimum inhibitory concentrations of Cefamandol and Ceftazidime, were determined, by tube method. These isolates were resistant to Ampicillin (Amp), Amoxicillin (Amo), Carbenicillin (Cb), Ticarcillin (Tic), Amoxicillin\ Potassium Clavulanate {Augmentin}, (Amo\CA), Ticarcillin\ Potassium Clavulanate {Timentin} (Tic\CA), Cefamandol (Cfm) and Ceftazidime (Cfz), also resistant to other antibiotics, such as Tetracycline, Chloramphenicol, Trimethoprim and (50% of the isolates were resistant to Nalidixic acid and Rifampicin). Transfer of plasmids  by direct conjugation experiments were performed by mating 10 strains  with recipient strain E.coliK12C  600 Rif or Nal resistant, and cell free b- lactamases were prepared and detected by macro-iodometric method. The activities of each cell free b– lactamases extract against Cfm and Cfz were determined by disks diffusion method (microbiological Masuda method) and by macro-iodometric method. The activity of b- lactamases was inhibited by the addition of Potassium Clavulanate. Conclusion:

Good effectiveness of Cfm\ CA and Cfz\ CA was obtained against resistant strains of E.coli due to complicated urinary tract infection (UTIs).

Key words: b- lactamases, Cefamandol, Ceftazidime, Timentin and  Augmentin .