In this study， tilapia fish scales were hydrolyzed by alkaline protease. The effects of heat treatment temperature， time and substrate concentration on protein recovery （PR）， degree of hydrolysis （DH） and angiotensin converting enzyme （ACE） inhibition rate before and after enzymolysis were investigated. The relative molecular mass distribution of the heat treated fish skin before and after enzymolysis was also characterized. The optimal extraction conditions in this study were as follows： heat treatment temperature was 121 ℃， time was 15 min， and substrate concentration was 2%. Under this conditions， PR and DH was 65.93% and 10.54%， respectively. Compared with untreated samples， PR and DH under the optimal heating treatment conditions showed increases of 78.29% and 89.23%， respectively. The ACE inhibition ratio was up to 73.80%， which was 66.78% higher than that of untreated samples. The collagen-based peptides below 5 ku accounted for 99%， which covers below 1 ku with a ratio of 39.46%.