The marine by-products from fish processing represent about 50% of the raw material but can be underutilized. In recent years, enzymatic hydrolysis of proteins from by-products have been reported to possess antioxidant activity. Protein hydrolysates that exhibiting antioxidant activity can be used for food preservation or to benefits human health. The objective of this study was to obtain and evaluate the antioxidant activity of the peptides present in the protein hydrolysates from Stripped weakfish by-products (Cynoscion guatucupa). The hydrolysate was obtained by enzymatic hydrolysis of a mixture of mechanically separated meat and cutting at a ratio of 10% (mprotein / v) using 2% protamex (pH 7.0 and 50 ° C) until a degree of hydrolysis of 15% (HP15) was achieved which monitored by the pH-stat method. The antioxidant activity was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities and iron reducing power assays in three concentrations of hydrolysate (1, 2.5 and 5 mg.mL-1). The HP15 showed a scavenging activity on DPPH radical of 45.5 ± 2.07%; 59.1 ± 1.24% and 72.9 ± 2.10%, and for reducing power assays values of 0.099 ± 0.01; 0.170 ± 0.02 and 0.279 ± 0.02, respectively. According to these results, it is observed that the antioxidant activity is dose-dependent to the hydrolysate concentration in both assays, demonstrating a direct correlation between antioxidant activities and reducing power, in the ability to donate electrons or hydrogen atom to reduce ferric iron (III) to ferrous iron (II). This may be due to the extent of hydrolysis leading to exposure of amino terminal groups and free amino acids with such capacity. Results suggesting that the HP15 from Stripped weakfish by-products possess potent antioxidant activities and might be used for food preservation and medicinal purposes. However, more detailed studies are required to explore their antioxidant ability.