Isolates of Pseudomonas aeruginosa (167) were obtained from 528 samples of canine otitis externa,identified by biochemical reactions and tested for susceptibility to 10 antimicrobials. The most effective drug was ciprofloxacin. The study reports alarming resistance among P. aeruginosa isolated from canine otitis externa samples in Rio de Janeiro, Brazil. Pseudomonas aeruginosa is a Gram-negative rod which is nonspore forming and aerobe. In dogs, P. aeruginosa have already been reported on otitis media/external infections (4, 6). The purpose of the present study was to determine the antimicrobial resistance of Pseudomonas aeruginosa isolates obtained from dogs with otitis externa in Rio de Janeiro, Brazil.Samples were obtained from 528 adult (≥ two years) dogs unmedicated for at least 15 days diagnosed with otitis externa (local pain, pruritus, erythema, ear discharge or desquamation).The samples were collected over a 2-year period (2007)(2008)(2009)). Cotton swabs were used to collect samples, inoculated