Disc and well diffusion methods were used to test the antibacterial activity of methanol extract and ethanol extract of the selected ethnomedicinal plant viz. Garcinia pedunculata Roxb. ex Buch.-Ham. Both the methanol extract and ethanol extract were subjected to antibacterial activity assay against the six clinical isolates. Antibiotic sensitivity test of the test bacteria against standard antibiotics were also determined. All the bacterial pathogens (Staphylococcus aureus, Enterococcus faecalis, Enterobacter cloacae, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae) were exposed to the plant extract in triplicates. The investigation revealed the potency of G. pedunculata extract as an effective antibacterial agent against both Gram-positive bacteria (GPB) and Gram-negative bacteria (GNB). G. pedunculata are evaluated to be bactericidal against the tested bacteria. The antibacterial activity may be due to an individual compound or synergistic effect of more than one compound present in the medicinal plant extract. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of the plant extracts were also investigated by using the broth microdilution method. HPLC-MS of the methanol extract of G. pedunculata fruit revealed the presence of Hydroxy Citric Acid Lactone (MW-190), Garcinone-E (MW-464), a-Mangostin (MW-410), β–Mangostin (MW-424), and γ-Mangostin (MW-396).