Nigella sativa L. seeds (N. sativa) have been used as a traditional remedy for a wide range of diseases including hypertension. The present study was performed to explore the effects of N. sativa oil on blood pressure (BP) in healthy volunteers. In a double-blind, randomized study, 70 healthy volunteers aged 34 to 63 years with systolic BP from 110 to 140 mmHg and diastolic BP from 60 to 90 mmHg were randomly allocated to receive 2.5 mL N. sativa oil or placebo two times a day for 8 weeks. The systolic and diastolic BPs, body mass index and blood levels of aspartate transaminase, alanine transaminase, alkaline phosphatase, creatinine and blood urea nitrogen were determined at baseline and endpoint. Results showed that in N. sativa oil treated group the systolic and diastolic BPs decreased significantly compared with baseline and placebo group at the endpoint. Other parameters did not significantly change in both groups at the endpoint. No adverse effects were reported. In conclusion, oral daily administration of 5 mL N. sativa oil to healthy volunteers for 8 weeks lowers systolic and diastolic BPs without any adverse effects. Copyright © 2013 John Wiley & Sons, Ltd.