Abstract: The synergistic effects of 23 selected phytochemicals (10 phenolic acids, 8 flavonoids and 5 alkaloids) in combination with oxacillin against laboratory passage-derived Vancomycin-intermediate Staphylococcus aureus (VISA) strain were investigated. Minimum Inhibitory Concentration (MIC) values of each of the phytochemicals and oxacillin were determined. Fractional Inhibitory Concentration (FIC) index of each combinations were evaluated using the checkerboard broth microdilution assay. Out of 23 phyto-oxacillin combinations, 14 (60.87%) were synergistic and 9 (39.13%) were additive. Flavonoid-oxacillin combination showed 87.5% synergism whereas alkaloid-oxacillin and phenolic acid-oxacillin, respectively exhibited 60 and 40% synergism. The range of FIC index values for synergistic interaction was between 0.0417-0.1333. The synergistic interaction between all the phytochemicals and oxacillin combinations demonstrated reduction in MIC value of oxacillin from 30 to 1.5 μg μL-1 except for quercetin, which markedly reduced the MIC value of oxacillin to 0.5 μg μL-1. Quercetin-oxacillin combination also displayed the lowest FIC index value of 0.0417. In conclusion, these findings suggested that flavonoid-based combination regimens may be useful candidate for treatment options of VISA infections.