Marine　byproducts　have　become　popular　research　themes　due　to　their　biological　significance.　The　black　sharkskin　protein　hydrolysate-based　antioxidant　peptides　were　firstly　investigated　in　this　study.　The　black　sharkskin-derived　novel　antioxidant　peptide　demonstrating　81.05%　free　radical　scavenging　activity　to　ABTS　at　500　μg/mL,　was　identified　to　be　Ala-Thr-Val-Tyr　(ATVY).　The　crucially　antioxidant　interaction　site　of　ATVY　action　on　ABTS　was　determined　to　be　Tyr　in　the　N-terminal.　ATVY　reacted　with　ABTS　to　generate　polyphenol-derived　adducts　which　subsequently　degraded　into　a　purple　compound.　The　MS/MS　showed　it　was　formed　by　covalently　bonding　through　the　phenol　group　of　ATVY　to　the　N　group　of　ABTS.　The　free　radical　scavenging　kinetics　of　ATVY　on　ABTS　demonstrated　a　two-phase　reaction　process.　These　findings　reveal　the　action　mechanism　of　ATVY　on　ABTS,　implying　ATVY　can　be　incorporated　in　the　production　of　antioxidant　food　additives.　©　2020　Elsevier　Ltd