Abstract: Background: Melastoma malabathricum is an important ethnomedicinal plant that has been rigorously studied for its medicinal properties, however, its closely related species, M. beccarianum has not been studied. Methodology: The phytochemical constituents of M. malabathricum and M. beccarianum were determined by gas chromatography mass spectrometry (GC/MS) analysis and their antimicrobial activities by agar-well diffusion method. Results: Similar chemical compositions were identified between the two Melastoma species, where three compounds were only detected in M. malabathricum methanol leaf crude extract, i.e., 8,11-octadecadienoic acid methyl ester, stearic acid methyl ester and tocopherol, whereas α-tocopherol-β-D-mannoside was only detected in M. beccarianum. The former was predominantly characterised by trans-squalene (17.02%) and the latter was by 5-hydroxymethylfurfural (15.76%). Both methanol extracts were found to exhibit antibacterial activities against Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. However, the extracts did not display antifungal activity against Saccharomyces cerevisiae under the conditions tested. Likewise, both aqueous leaf crude extracts did not show any detectable antibacterial activities. Conclusion: This study not only supported the close relatedness of M. malabathricum and M. beccarianum in terms of their phytochemical constituents and antimicrobial properties but also showed that these species were still uniquely different from each other.