Pseudomonas is a group of bacteria found in soil, water, skin flora and most man- made environments throughout the world. In this study, the resistance mechanisms of 16 clinical P. aeruginosa isolates from the Royal Care Hospital, Coimbatore city, Tamilnadu. All the samples were inoculated onto selective mediums for isolation of pseudomonas spp. and for isolation of pseudomonas aeruginosa. Various types of specific media were prepared to cultivate and characterize isolates, such as; Blood agar, Nutrient agar for all isolates. A pseudomonas aeruginosa isolate was selected for further studies taking one pseudomonas aeruginosa from each of the source and were identified by biochemical characteristics. Bacteria obtained from urine samples were cultured and tested for antimicrobial susceptibility to 16 kinds of antibiotics. Urine samples were cultured on different media and incubated, thereafter bacteria were isolated and purified by streaking four times on the same media; isolates were identified depending on morphological, microscopic, and biochemical characteristics. The isolated strains of bacteria were tested for their susceptibility to some antibiotics using disk diffusion method. The antagonistic activity was evaluated by observing a clear zone of inhibition growth. For all the three strains Antibiotic susceptibility testing (AST) was carried out to determine the antibiotic sensitivity and resistant in plate culture conditions. In antibiotic susceptibility testing, Gentamycin and Amoxicillin was sensitive against majority of isolates 80% effective, followed by Levofloxacin and Amikacin 70% and Chloramphenicol 50%, Nitrofurantoin 40% and marked resistance was observed to commonly used drugs like both Ceftriaxone and Amoxicillin 30%, less effectiveness showed by Cefixime 10%. Other Pseudomonad’s also showed good sensitivity against antibiotics.