Squid viscera, one of the major by-products in squid processing, were hydrolyzed to generate bioactive autolysates using their endogenous proteases. In vitro antioxidative activities of squid viscera autolysates (SVAs) were evaluated. The SVAs demonstrated strong activity on scavenging 1,1-diphenyl-2-picrylhydrazil (DPPH) and hydroxyl radicals, as well as reducing power ability. The SVAs were purified using size exclusion chromatography and RP-HPLC. Nineteen peptides were identified in the active fraction SVAs3 by liquid chromatography-electrospray ionization/multi-stage. mass spectrometry (LC-ESI-Q-TOF-MS/MS). Among these identified peptides, six peptides with relatively small molecular weights (700-800 Da), LLAPPER, FPGLADR, WVAPLK, FFNPVH, FNVVLK and LELPLK, were synthesized for assaying antioxidative activity in vitro. Peptide WVAPLK demonstrated strong scavenging effects on free radicals, with the IC50 values of 0.82 +/- 0.08 mg/mL (or 1.14 +/- 0.11 mM) for DPPH radical and 1.85 +/- 0.04 mg/mL (or 2.60 +/- 0.06 mM) for hydroxyl radical, respectively. The low molecular weight and hydrophobic residue W at the N-terminus and basic residue K at the C-terminus as well as specific residues P and L within sequence should play a key role for the high antioxidative activity of WVAPLK. The results suggested that the SVAs could be used as a source of antioxidants and peptides. (C) 2016 Elsevier Ltd. All rights reserved.