This work determined the ability of hemp seed meal protein hydrolysate (HMH)-containing diets to attenuate elevated blood pressure (hypertension) development in spontaneously hypertensive rats (SHRs). Effects of diets on plasma levels of renin and angiotensin I-converting enzyme (ACE) in the SHRs were also determined. Methods: Defatted hemp seed protein meal was hydrolyzed using simulated gastrointestinal tract digestion with pepsin followed by pancreatin, and the resulting HMH used as a source of antihypertensive peptides. The HMH was substituted for casein at 0.5 and 1.0 % levels and fed to young growing rats for 8 weeks (preventive phase) or adult rats for 4 weeks (treatment phase). Results: Feeding of young growing SHRs with HMH resulted in attenuation of the normal increases in systolic blood pressure (SBP) with an average value of ~120 mmHg when compared to the casein-only group of rats (control) with a maximum of 158 mm Hg (p < 0.05). Feeding adult rats (SBP ~145 mmHg) with same diets during a 4-week period led to significant (p < 0.05) reduction in SBP to ~119 mmHg in comparison with 150 mmHg for the control rats. Plasma ACE activity was significantly (p < 0.05) suppressed (0.047-0.059 U/mL) in HMH-fed rats when compared to control rats (0.123 U/mL). Plasma renin level was also decreased for HMH-fed rats (0.040-0.054 'g/mL) when compared to control rats that were fed only with casein (0.151 'g/mL).Conclusions: The results suggest that HMH with strong hypotensive effects in SHRs could be used as a therapeutic agent for both the prevention and treatment of hypertension.