Background: Medicinal plants have now attracted more attention due to their antibacterial activity and also increasing antibiotic resistance among bacteria. Native plants of each region are potential resources for this purpose.Objectives: The aim of the present study was to detect the antibacterial effect of Eucalyptus microtheca (Myrtaceae family) which is currently used as an antibacterial fumigation medicine.Materials and Methods: Using standard disk diffusion method, the antibacterial activity, MIC, and MBC indexes of alcoholic extracts from this plant were tested on some pathogenic bacteria. The structural changes following the exposure to these extracts were also investigated in test bacteria.Results: Significant antibacterial activity was found against gram-positive and gram-negative bacteria, which among them, Escherichia. coli andPseudomonas. aeruginosa showed the most sensitivity and Staphylococcus. aureus the least. The value of MIC and MBC for both extracts was 8 mg/mL forE. coli, while they were 8 mg/mL and 16 mg/mL for Bacillus cereus, respectively. Both MIC and MBC values of methanolic and ethanolic extracts againstP. aeruginosa were 8 and 16 mg/mL respectively. SEM revealed structural changes in the affected bacteria that suggest the cell wall was the main target site of active constituents.Conclusions: It can be concluded that this plant has potential application in infection control, especially against E. coli and P. aeruginosa and regarding their recent reported epidemic, this plant can be a good choice for antibiotic discovery.