Portugal is one of the largest consumers of fishery products in Europe. This consumption involves a large amount of discarded raw material, such as rejected fish in selling auctions and the generation of by-products in industrial production processes. The by-products in the canning industry alone reach 40% of the raw material, while the frozen fish industries may reach 10-50% of the raw material (INE, 2013). Fish protein hydrolysates (FPH) are one of the most promising technologies for the recovery of these by-products (Kristinsson e Rasco, 2000). The present study aims to investigate the effect of different enzymes (0.5% Alcalase and 0.5% Neutrase®) and hydrolysis time (0, 60 and 120 minutes) in the characteristics of FPH obtained from mackerel canning by-products. The hydrolysates were characterized determining the nitrogen recovery, the degree of hydrolysis (DH), the fat recovery, the DPPH free radical scavenging activity, moisture and ash content. Nitrogen recovery was significantly higher in FPH produced with Alcalase (17.35%) than in FPH produced with Neutrase® (3.58%). FPH produced using Neutrase® presented a higher DH, suggesting that this enzyme had a preference for soluble protein, whereas Alcalase will preferentially hydrolyze insoluble protein contained in the by-products. The FPH produced with 0.5% of Alcalase® and 120 minutes showed the higher DPPH free radical scavenging activity (35.85±1.1%). It was observed that after 90 minutes of hydrolysis, DPPH free radical scavenging activity increased in almost all mackerel hydrolysates by 5.24%. The results suggest that FPH may add value to currently discarded products and, furthermore, may enable the development of new functional products. The FPH may allow the transformation of previously low commercial value by-products into a source of profit. Instituto Nacional de Estatística (INE), I. P. (2013), Estatísticas da Pesca 2012, Edição 2013, Lisboa, Portugal. Kristinsson, H. G.; Rasco, B. A. (2000). Fish Protein Hydrolysates: Production, Biochemical and Functional Properties Critical Reviews, in Food Science and Nutrition, 40: 43-81.