Nigella sativum which belongs to the family Ranunculaceae, is one of the important medicinal plant species. The present study aimed to assess antioxidant- related effects of Nigella sativum in human volunteers and its effects on liver, renal and cardiac function tests. 9 healthy volunteers participated in the study and each received 1 spoon from ground seeds of Nigella sativum daily for five days. Blood samples were taken before and 1 hour after the administration of 1 spoon from ground seeds of Nigella sativum (samples 1 and 2, respectively) and then one day after the last dose of day five (sample 3). The first blood taken before the first dose (sample 1), served as the control for the next samples (2 & 3). Serum total antioxidant status (TAS), erythrocyte reduced glutathione (GSH), malonyldialdehyde (MDA), and serum selected biochemical tests were used as assays. Oral administration of ground seeds of Nigella sativum to healthy volunteers, for five days increased the serum TAS and serum erythrocyte GSH significantly, with no impact on serum biochemical tests for kidney, liver, cardiac and pancreatic parameters. In conclusion, as the current outcomes are based on healthy humans with no oxidative stress, this shows that oral administration of ground seeds of Nigella sativum can improve the baseline of the defense mechanisms against possible oxidative stress, with no adverse effects, thus decreasing susceptibility or preventing the progress of pathological conditions related to oxidative stress.