Cauliflower by-products (stems and leaves) are rich in leaf protein. Making full use of cauliflower by-products can not only alleviate the shortage of protein resources but also be beneficial to the environmental protection. This study sought to prepare and purify an angiotensin I-converting enzyme (ACE) inhibitory peptide from cauliflower by-products protein hydrolysate. Our result showed that the highest ACE inhibitory activity was observed in the Alcalase 2.4 L hydrolysate among tested hydrolysates (pepsin, pancreatin, and Alcalase 2.4L). After purification, a dipeptide (Val-Trp) was identified, with a molecular weight of 304.1665 Da. This peptide had a potent ACE inhibitory activity with IC50 of 31.30 mu M. Based on this purification process, approximately 42 mg of this dipeptide was obtained from 1 kg of fresh cauliflower by-products. Overall, the results suggest that cauliflower by-products protein can be used as an economical source of functional food material against hypertension. (C) 2016 Elsevier Ltd. All rights reserved.