Angiotensin I-converting enzyme (ACE) inhibitory peptides from digested Porphyra yezoensis protein were purified with ultrafiltration and ionic exchange. The hydrolysate of Porphyra yezoensis protein was ultrafiltered by 10 kDa and 3 kDa membrane in sequence. It was found that the IC50 value of Porphyra yezoensis peptides decreased from original 0.844 mg/mL to 0.523 mg/mL. And Nakai D61 cation resin was selected according to its largest absorption in the ionic exchange static absorption test. The results showed that the second elution peak had the highest protein recovery, ACE inhibitory activity recovery and the lowest IC50 value, which were 45.2%, 61.5% and 0.127 mg/mL, respectively. The sample’s IC50 value decreased by 75.7% after the ionic exchange purification.