Peptide hydrolysates of silkworm pupae protein with molecular weight of less than 5000 Da were prepared by ultrafiltration. The extracted peptide hydrolysates of silkworm pupae protein had inhibitory action on angiotensin-I-converting enzyme activity in vitro. The hydrolysates were orally administered to spontaneously hypertensive rats (SHR) in one period and long-term (four weeks). The results showed that the systolic blood pressure (SBP) of the treatment groups decreased in a dose-related manner. After one oral administration of silkworm protein hydrolysates with doses of 60, 20 and 5 mg/kg, the SBP of SHR decreased by 21.5, 13.8, and 9.0 mmHg in 1.5 h. After four weeks of the treatment in 80 mg/kg, the SBP decreased by 25 mmHg, with the antihypertensive activity close to 4 mg/kg of captopril; the SBP of the 40 mg/kg dose group also decreased by 17.5 mmHg. The peptide hydrolysate did not affect the SBP in normal, non-hypertensive rats in one period and long-term treatments. The acute toxicity research showed that the peptide hydrolysates were safe and without side effects. This research would be helpful in exploring the silkworm protein peptides as functional components for the antihypertension treatment.