---

In this study, gelatin was first extracted by alkaline and acidic treatment including 0.19 N NaOH and 0.12 N acetic acid solution by ratio of skin of rainbow trout (Oncorhynchus mykiss (to solution of 1 to 7 and then heat treatment in 50 °C. Then, hydrolysed by alcalase enzyme for 4 hours with the ratio of enzyme to the substrate 1 to 100 and the degree of hydrolysis were measured after 4 hours. DPPH and ABTS free radical scavenging activity, as well as reducing power assay of gelatin hydrolysate were measured. The results showed that the degree of hydrolysis after 4 hours was 46/7%. Also the highest DPPH and ABTS free radical scavenging and reducing power at concentration of 10 mg/ml were 39/8%, 50/7%, and 0/123, respectively. The skin from fish filleting can be a suitable raw material for extraction of peptides with biological activities. The results showed that peptides derived from rainbow trout fish skin gelatin can be considered as a natural antioxidant.