In the present paper, bioactive peptides from cauliflower by-products (leaves and stems) were investigated. Alcalase® protein hydrolysis time and pH conditions were optimized, then the hydrolysates were fractionated by preparative RP-HPLC into 12 fractions. Each fraction was tested for the ABTS (2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)), and DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity and for ACE (angiotensin-converting enzyme) inhibitor activity. The peptides in the most active fractions were identified by peptidomics technologies and screened for bioactivity by the use of bioinformatics. For ACE-inhibitor activity, two peptides were synthetized, APYDPDWYYIR and SKGFTSPLF, which provided an EC₅₀ value of 2.59 μmol L⁻¹ and 15.26 μmol L⁻¹, respectively. For the ABTS radical scavenging activity, SKGFTSPLF and LDDPVFRPL were tested, and provided an EC₅₀ of 10.35 μmol L⁻¹ and 8.29 μmol L⁻¹, respectively. For the DPPH radical scavenging activity, SKGFTSPLF and LRAPPGWTGR were tested and provided an EC₅₀ of 8.2 μmol L⁻¹ and 5.26 μmol L⁻¹, respectively.