Background and objective: Melaleuca viminalis (syn. Callistemon viminalis, red bottle brush) and Melaleuca armillaris (white Bottle brush) belong to the family Myrtaceae and are reported for their traditional medicinal properties. The objective of this study was to explore and compare the chemical compositions and biological properties of these two species.Methods: Sequential extraction and hydro-distillation methods were employed to extract essential oils for further analysis of chemical composition by gas chromatography-mass spectrometry (GC-MS). The biological potential as antioxidants was investigated for both species by assessing 1,1-diphenyl-2-picrylhydrazyl (commonly known as DPPH) scavenging activity and by use of ferric iron reducing assay. The biological potential as antibacterials was investigated by agar well diffusion assay. The in vitro cytotoxicity analysis was carried out by MTT assay.Results: GC-MS analysis of the essential oil of Melaleuca viminalis indicated the presence of eucalyptol as the principal chemical constituent, while that of Melaleuca armillaris indicated the presence of methyl eugenol. Comparative studies indicated that Melaleuca viminalis had higher potential for antioxidant and antibacterial activities than Melaleuca armillaris. Also, the essential oil of Melaleuca viminalis exhibited in vitro cytotoxicity against the cancer cell lines of A549 (lung; IC 50 24.12 µg/mL), HCT-116 (colon; IC 50 21.5 µg/mL) and T47D (breast; IC 50 21.78 µg/mL), in comparison to Melaleuca armillaris for which cytotoxicity was only observed against theA549 (IC 50 10.2 µg/mL) lung cancer cell line. Conclusions:The present findings suggest that essential oil of Melaleuca viminalis (leaves) hold potential for future application in various medical procedures. However, the presence of methyl eugenol in Melaleuca armillaris raises concern of its being acarcinogenic compound, so further detailed toxicological studies are required to validate its therapeutic potential.