Background: Pseudomonasaeruginosais ubiquitous in nature and it is found as a commensal in the skin and gastrointestinal tract of humans. It causes opportunistic infections in immune-compromised patients, not commonly seen in immune-competent patients. Peppermint oil has antibacterial activity against both gram positive and gram-negativebacteria.Aim of the study is to determine the antibacterial activity of peppermint oil against isolates of Pseudomonas aeruginosa. Materials and method: 20 quantity of isolates of pseudomonas aeruginosa which are non-repetitive were collected. Isolates were preserved in semi-solid trypticase soy broth stock and stored at 4oC until further use. Antibiotic susceptibility testing was found for these twenty isolates to commonly used antibiotics such as to piperacillin-tazobactam, cefotaxime, ceftazidime, tetracyclin, cotrimoxazole, aztreonam, gentamicin and imipenem by Kirby Bauer disc diffusion method. Anti-bacterial activity of peppermint oil was tested against P. aeruginosa isolates by minimum inhibitory concentration method. Results:40% of isolates were inhibited at 0.06%, 25% of isolates were inhibited at 0.125% of essential oil, 20% of isolates was inhibited at 0.25% of essential oil and 5% of isolates were inhibited at 0.5% of essential oil. Thus, the Minimal inhibitory concentration of peppermint oil against P. aeruginosa was found to be 0.06%. Conclusion:The peppermint oil is found to have antibacterial activity against P. aeruginosa. However, the studies on toxic and irritant properties of essential oils are imperative, especially when considering any new products for human administration.