To compare the antibacterial activity of the Australian tea tree oil (TTO) with various other medicinally and commercially important essential myrtaceous oils (cajuput oil, niaouli oil, kanuka oil, manuka oil, and eucalyptus oil) the essential oils were first analysed by GC-MS and then tested against various bacteria using a broth microdilution method. The highest activity was obtained by TTO, with MIC values of 0.25% for Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Salmonella choleraesuis, Shigella flexneri, Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus, S. saprophyticus, and S. xylosus. It is noteworthy that manuka oil exhibited a higher activity than TTO against gram-positive bacteria, with MIC values of 0.12%. Both TTO and manuka oil also demonstrated a very good antimicrobial efficacy against various antibiotic-resistant Staphylococcus species. Pseudomonas aeruginosa was resistant to all essential oils tested, even at the highest concentration of 4%.