The incorporation of natural antioxidants into food systems is one of the most effective approaches to prevent proteins oxidation induced by peroxyl radicals. The goal of this research is to investigate the influences of (−)-epigallocatechin-3-gallate (EGCG) on the physicochemical properties, structural characteristics and interfacial properties of α-lactalbumin (α-LA) under oxidative stress induced by peroxyl radicals. Increasing peroxyl radicals (1–10 mmol/L AAPH) dramatically caused the loss of carbonyl, free amine and free sulfhydryl groups, water solubility and fluorescence intensity of α-LA but the increase of surface hydrophobicity. At 1 mmol/L AAPH (low), the increase of EGCG would further decrease free amine groups and water solubility, leading to the formation α-LA aggregates, and the gradual enhancement of emulsifying stability index (ESI) from 73% to 85% and foaming stability (FS) from 61% to 68%. At 5 mmol/L AAPH (medium), the increase of EGCG also facilitated the improvement of ESI and FS of α-LA. At 10 mmol/L AAPH (high), the impacts of EGCG on structure characteristics and interfacial properties of α-LA were highly dose-dependent. This study provides some useful information on the application of polyphenols in retarding the oxidation of milk proteins during food processing.