||Oxidative stress plays significant role in pathophysiologic events of acute and chronic diseases. Intracellular biomolecules such as lipids, proteins and nucleic acids are damaged via oxidation by excessive active oxygen species (AOS). Protease inhibitor was isolated and purified from the fruits of Solanum aculeatissimum Jacq. (SAPI) via four sequential step procedure i.e., salt precipitation to Sepharose affinity chromatography. Subsequently, the antioxidant power is analysed using DPPH, H2O2, O2.-, ABTS, OH. radical scavenging activity, reducing power potential, metal chelating ability and FRAP (Ferric reducing antioxidant power) method. SAPI exhibited significant IC50 values for most of the AOX assays. DPPH radical scavenging, reducing power, metal chelating ability, ABTS and OH. radical scavenging activity were comparable with the synthetic antioxidants like ascorbate and BHT. Further studies are warranted to trace the molecular mechanism of AOX activity by SAPI using in vivo animal models.