The aim of the present study was the evaluation of the antibacterial activity of Mentha pulegium essential oil on isolates of Klebsiella. Thirty nine isolates were collected from urine specimens submitted to two educational hospitals in Urmia, Iran. The susceptibility of isolates was determined using a broth microdilution method. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of isolates to Mentha pulegium essential oil were determined. The susceptibilities of isolates to different antibiotics were tested using agar disk diffusion method. The rates of resistance were determined to antibiotics as follows: gentamicin 46.1%, tobramycin 48.7%, ceftizoxime 41%, co-trimoxazole 46.1%, amikacin 33.3%, cephtazidime 51.3%, ciprofloxacin 30.8%, kanamycin 53.8%, nalidixic acid 30.8% ampicillin 79.5% and nitrofurantoin 41%. Mentha pulegium essential oil possessed antibacterial effect against all isolates of Klebsiella sp. with MIC and MBC values in the range of 1.9 x 10(-3) to 4.9 x 10(-4) mm3 mm(-3). In this study clinical isolates of Klebsiella sp. showed very high resistance to tested antibiotics. These results suggest the potential use of the Mentha pulegium essential oil for the control of multi-drug resistant Klebsiella sp. infections. However, more adequate toxicological study must be carried out to verify the possibility of using it for fighting microorganisms in human.