Objectives: To evaluate the phytochemical composition and the antioxidant activity of aqueous-methanolic (20:80) leaves extract of Mundulea sericea Willd. Methods: The extract of leaves was tested for antioxidant activity using various in vitro models viz., 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide, ABTS, ferric reducing antioxidant power (FRAP), total antioxidant activity and reducing power. The phytochemical composition (GC-MS and HPLC) along with total phenolic and flavonoid content of the extract at different concentrations were also determined. Results: Total phenolic and flavonoid contents were found to be equivalents to 107.86 ± 0.53 μg of gallic acid and 44.53 ± 0.156 μg of rutin /mg of dried hydro-methanolic methanolic extract, respectively. Among various antioxidant assays performed, maximum inhibition was observed for ABTS (IC50 13.26 ± 0.396 μg) followed by DPPH (IC50 79.83 ± 0.306 μg) and NO (IC50 6.35 ± 0.23 μg/mL) assay. The GC-MS analysis revealed over 38 compounds; the prevailing compounds were Sec- Butyl ethyl sulfoxide and Di-methyl sulfoxonium formyl methylide. The RP-HPLC analysis further confirmed the presence of rutin, cinnamic acid and salicylic acid. Conclusion: The results of the present study demonstrated that Mundulea sericea leaves possess high phenolic with flavonoid contents and also revealed potential antioxidant activity so these leaves could be used as a viable source of natural antioxidants for industrial and pharmaceutical preparations.