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• The extraction rate of green tea protein from green tea residue under the optimised enzyme-alkali complex method was 74.27 %. • The ACE inhibitory rate of the green tea proteolytic product under the optimised hydrolysis condition was determined to be 77.00 %. • The molecular weight distribution of the polypeptide in the green tea proteolytic product was widely between 45.0–1.2 kDa. • The green tea proteolytic product had good blood pressure lowering activity in vivo. Green tea contains active ingredients which are beneficial for health. While numerous studies have been conducted on the components extracted from green tea, few studies have investigated the active ingredients in tea residue. In this study, proteins were extracted from green tea residue via an optimised alkaline extraction combined with enzymatic hydrolysis, of which, an acidic protease was selected to prepare an enzymatic hydrolysate because of its high angiotensin converting enzyme (ACE) inhibitory activity. The composition characteristics of extracted green tea proteolysis products were elucidated, including amino acid composition, molecular weight distribution and possible amino acid sequences. In addition, the protein hydrolysate had anti-digestive properties, maintained its activity of inhibiting ACE enzyme at different temperatures, pH and metal ions, and exhibited antihypertensive activity in animals. In conclusion, the optimised alkaline extraction and enzymatic hydrolysis conditions of a ACE inhibitory peptide from green tea residue is an optimal extraction method to maintain its antihypertensive activity, providing the basis for the clinical application of green tea for blood pressure reduction. [ABSTRACT FROM AUTHOR]