► This study was to purify an antioxidative peptide derived from Chlorella ellipsoidea. ► Protein derived the C. ellipsoidea was hydrolyzed using different proteases. ► We investigated using free radical scavenging assay by ESR spin-trapping technique. ► Protective abilities of purified peptide in radical-induced cell damage were tested. ► The peptide has a good dietary supplement for the prevention of oxidative stress. Protein derived the marine Chlorella ellipsoidea was hydrolyzed using different proteases (papain, trypsin, pepsin and α-chymotrypsin) for production of antioxidative peptide, and the antioxidant activities of their hydrolysates were investigated using free radical scavenging assay by electron spin resonance spin-trapping technique. Among the hydrolysates, the peptic hydrolysate exhibited the highest antioxidant activity compared to other hydrolysates. To identify antioxidant peptide, the peptic hydrolysate was purified using consecutive chromatographic methods, and the antioxidant peptide was identified to be Leu-Asn-Gly-Asp-Val-Trp (702.2Da) by Q-TOF ESI mass spectroscopy. The antioxidant peptide scavenged peroxyl, DPPH and hydroxyl radicals at the IC50 values of 0.02, 0.92 and 1.42mM, respectively. The purified peptide enhanced cell viability against AAPH-induced cytotoxicity on normal cells. Furthermore, the purified peptide reduced the proportion of apoptotic and necrotic cells induced by AAPH, as demonstrated by decreased sub-G1 hypodiploid cells and decreased apoptotic body formation by flow cytometry.