Angiotensin-converting enzyme (ACE, EC 3.4.15.1) is a physiological target for researching new antihypertensive drugs, as it is a substantial enzyme in the regulation of blood pressure. Herein, ACE was purified from human serum with affinity chromatography. Vmax and KM values were found as 60.98 (µmol/min)/mL and 0.34 mM, respectively. The effects of Gly-Arg-Gly-Asp-Ser (GRGDS) and Arg-Gly-Asp (RGD) bioactive peptides on purified ACE were researched. Also, captopril, a specific ACE inhibitory, was used as a reference inhibitor. Bioactive peptides, GRGDS and RGD, demonstrated the inhibitory effect on purified ACE with $IC_{50}$ values of 46.39 µM and 456.46 µM, respectively. Ki values and kind of inhibition for GRGDS and RGD by the Lineweaver-Burk chart were found. The kind of inhibitory for these bioactive peptides was calculated as reversible-competitive inhibitory. Ki values for GRGDS and RGD were obtained as 93.28 µM and 435.67 µM, respectively. The $IC_{50}$ value of captopril was designated as 1.57 nM. The inhibitory kind of captopril was designated as reversible non-competitive inhibitory and the Ki value was 0.99 nM. In this study, it was concluded that RGD and GRGDS bioactive peptides have the potential to be utilized as ACE inhibitors.