Hypertension and oxidant stress predispose to the onset and progression of arteriosclerotic diseases. In this study, the components of two kinds of porcine liver hydrolysates (LH-I and LH-II) were analyzed, and the antioxidant effects and angiotensin converting enzyme (ACE)-inhibiting effects of LH-I and LH-II were examined in vitro. Furthermore, the effects of LH-I and LH-II on the blood pressure were examined in spontaneously hypertensive rats (SHR). The results showed that peptides and amino acids accounted for 70% or more of the constituents of both LH-I and LH-II. The results of gel filtration HPLC showed that most of the nitrogen-containing components were peptides or amino acids with molecular weights of 6000 or less. The DPPH radical scavenging activities of LH-I and LH-II were 55.6 and 38.1 μM Trolox Equivalent/g, respectively. The IC(50) values for the ACE-inhibiting activity of LH-I and LH-II were 0.18 and 0.31 mg/mL, respectively. Oral administration of 1 g/rat of LH-I or LH-II to SHR resulted in significant lowering of the blood pressure. These findings indicate that both LH-I and LH-II have antioxidant activity and ACE-inhibiting activity. Moreover, both exerted a blood pressure-lowering effect in SHR. The antioxidant activity and ACE-inhibiting activity of LH-I and LH-II are presumed to be based on the actions of the component peptides.