Angiotensin-converting enzyme (ACE) inhibitory activity and antihypertensive activity of bovine and porcine collagen hydrolysates in spontaneously hypertensive rats (SHR) were investigated. The hydrolyzed collagens were subjected to ultrafiltration using membranes with cutoffs of 30-50 kDa (permeate P1), 5-8 kDa (permeate P2), or 1-2 kDa (permeate P3) in order to obtain products with a narrower range of molecular size. The hydrolyzed bovine and porcine collagens and their permeates showed low ACE inhibitory activity (50% inhibitory concentration [IC(50)] = 5.42-15.58 mg of protein/mL). However, after in vitro gastrointestinal digestion, a significant increase in the ACE inhibitory potency of the hydrolyzed collagens was observed (IC(50) = 0.97-4.02 mg of protein/mL). Permeates had a higher ACE inhibitory activity and hypotensive activity than non-ultrafiltered hydrolysates. The P1 permeate of bovine and porcine collagen and the P3 fraction of the porcine collagen hydrolysate exhibited the best antihypertensive activity in vivo, promoting a maximum reduction in blood pressure of 22 mm Hg, 21.33 mm Hg, and 21.33 mm Hg, respectively, while lisinopril promoted a maximum reduction of 51.00 mm Hg. These results suggest that the commercial collagen hydrolysates of bovine and porcine origin may be a potential source of bioactive peptides.