Introduction: Propolis is a complex resinous mixture collected by bees from plant exudates(sap) and mixed with beeswax and pollen. It is known that propolis possesses antimicrobial, antioxidative and anticancer activities. Therefore, propolis has attracted much attention in recent years as a potential substance used in medicine. The aim of this study was to determine the antibacterial properties of ethanol extract of propolis (EEP), collected in Khorasan, against Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa. Materials and methods: Pulverized raw propolis (2 g) placed inside a paper timber was submitted to 8h Soxhlet extraction at a maximum temperature of 70 °C, using 250 mL of ethanol (98%). The resulting extracts were evaporated in a rotary evaporator with thermostatic bath (70°C) to obtain the dry extract and store at 4°C until use. The minimum inhibitory concentration (MIC) of EEP (dissolved in 4%v/v DMSO) against four pathogenic bacteria was evaluated by broth microdilution method in a range of 0.5-4 mg/ml. The MBC was determined by the lowest concentration that kills 99.9% of the initial bacterial population. Results: The MIC values of EEP against E. coli, S. aureus and B. subtilis were calculated to be 2,2 and 4 mg/ml, respectively. The MBC values of EEP were the same as MIC. No significant antibacterial properties were determined against P. aeruginosa. Results exhibited that, EEP had better inhibitory effect on Gram positive bacteria than Gram negative bacteria. Conclusion: EEP showed good antimicrobial activity against tested pathogens. It appears that propolis could be considered as an antimicrobial agent in several materials such as wound band, toothpaste and etc.

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