Pseudomonas aeruginosa is an opportunistic pathogen and the leading cause of nosocomial infection worldwide. This bacterium produces enzymes known as extended spectrum β-lactamases which render broad spectrum cephalosporins and penicillins inactive. This study reports antibiotic susceptibility pattern, multiple antibiotic resistance (MAR) index and prevalence of extended spectrum β-lactamases among clinical isolates of P. aeruginosa collected from tertiary care hospitals of Peshawar, Pakistan.A total of 187 P. aeruginosa isolates were collected. Antibiotic susceptibility was evaluated by Kirby Bauer disc diffusion method using nineteen different antibiotics and multiple antibiotic resistance (MAR) index was determined. Prevalence of extended spectrum β-lactamases was studied by double disc synergy test. The ESBL genes blaCTX-M, blaOXA-10, blaPER-1, blaSHV and blaTEM were analyzed by PCR amplification among the isolates. Susceptibility to antibiotics was: imipenem (85.02%), meropenem (82.88%), cefepime (76.47%), piperacillin-tazobactam (76.47%), colistin (74.86%), ciprofloxacin (74.33%), piperacillin (72.19%), ceftazidime (68.98%), ofloxacin (68.44%), amikacin (66.84%), cefoperazone (66.31%), carbenicillin (66.31%), gentamicin (64.7%), tobramycin (64.7%), aztreonam (52.4%), ticarcillin (42.78%), ceftriaxone (32.08%), cefotaxime (15.5%), amoxicillin-clavulanic acid (6.41%). A total of 36.89% (n=69) isolates showed multi drug resistance. The MAR index of 34.22% (n=64) isolates was higher than 0.2. Phenotypic ESBL production was observed in 21.39% (n=40) isolates. Prevalence of blaOXA-10, blaCTX-M, blaTEM and blaSHV was 36.89% (n=69), 20.85% (n=39), 5.34% (n=10) and 3.2% (n=6) respectively. PER-1 gene was not detected. Resistance to antibiotics is increasing in P. aeruginosa which is a matter of concern and needs proper management. Non-selective and over use of antibiotics should be avoided and proper control measures should be taken to avoid the spread of these multi-drug resistant strains.