In addition to the neural and autoregulatory factors, blood pressure (BP) is regulated by humoral factors including vasoactive peptides. When evaluating the peptide actions, degradation by proteases should be also considered in addition to the generation of peptides and their receptors. This review describes the roles of aminopeptidase A, placental leucine aminopeptidase and kininase I, which are enzymes responsible for hydrolyzing angiotensin II (AngII), vasopressin (AVP) and bradykinin (BK), respectively, in BP regulation. Especially, we focus on the association of the proteases with preeclampsia, hypertensive disorder peculiar to pregnancy, since one of the representative organs that are rich in theses proteases is placenta. Although the physiological roles of the placental proteases have not been fully understood, several lines of evidence suggest that the proteases are involved in the maintenance of pregnancy homeostasis including fetal and maternal BP regulation through the metabolism of bioactive peptides at the interface between mother and fetus.