Objective:To evaluate the effect of Nigella sativa(NS) extract on memory performance and its possible mechanisms in scopolamine(Sco)-induced spatial memory impairment model using Morris water maze test.Methods:Thirty-two male Wistar rats were randomly divided into four groups.The control group received saline instead of both NS extract and Sco.The Sco group was treated by saline for two weeks,and was injected by Sco(2 mg/kg,intraperitoneally) 30 min before each trail in Morris water maze test.Sco+NS 200 and Sco+NS 400 groups were daily treated by 200 or 400 mg/kg of NS(intraperitoneally) for two weeks,respectively,and were finally injected by Sco30 min before Morris water maze test.The brains of animals were removed to determine the acetylcholinesterase(AChE) activity and oxidative stress criteria in cortical tissues.Results:Time latency and path length in the Sco group were significantly higher than in the control group(P<0.01),while the Sco+NS 400 group showed a significantly shorter traveled path length and time latency compared with the Sco group(P<0.01).AChE activity in the cortical tissues of the Sco group was significantly higher than the control group(P<0.01),while AChE activity in the Sco+NS200 and Sco+NS 400 groups was lower than the Sco group(P<0.01).Following Sco administration,malondialdehyde(MDA) concentrations were increased(P<0.01) in comparison with the control group,while cortical total thiol content decreased(P<0.01).Pretreatment with extracts caused a significant elevation in cortical total thiol content(P<0.01)and reduction in cortical MDA concentration(P<0.01) compared with the Sco group.Conclusions:Hydro-alcoholic extract of NS prevents Sco-induced spatial memory deficits and decreases the AChE activity as well as oxidative stress of brain tissues in rats.Our results support the traditional belief about the beneficial effects of NS in nervous system.Moreover,further investigations are needed for better understanding of this protective effect. Objective: To evaluate the effect of Nigella sativa (NS) extract on memory performance and its possible mechanisms in scopolamine (Sco) -induced spatial memory impairment model using Morris water maze test. Methods: Thirty-two male Wistar rats were randomly divided into four groups. The control group received saline instead of both NS extract and Sco. The Sco group was treated by saline for two weeks, and was injected by Sco (2 mg / kg, intraperitoneally) 30 min before each trail in Morris water maze test. Sco + NS 200 and Sco + NS 400 groups were daily treated by 200 or 400 mg / kg of NS (intraperitoneally) for two weeks, respectively, and were finally injected by Sco30 min before Morris water maze test. The brains of animals were removed Results: Time latency and path length in the Sco group were significantly higher than in the control group (P <0.01), while the Sco + NS 400 group showed a significantly shorter traveled path length and time latency compared with the Sco group (P <0.01). AChE activity in the cortical tissues of the Sco group was significantly higher than the control group (P <0.01) while AChE activity in the Sco + NS200 and Sco (P <0.01) in comparison with the control group, while cortical total thiol content decreased (P <0.01) .Pretreatment with extracts caused a significant elevation in cortical total thiol content (P <0.01) and reduction in cortical MDA concentration (P <0.01) compared with the Sco group. Conclusions: Hydro-alcoholic extract of NS prevents Sco-induced spatial memory deficits and decreases the AChE activity as well as oxidative stress of brain tissues in rats. Our results support the traditional belief about the beneficial effects of NS in nervous system. Moreover are further investigations needed for better understanding of this protective effect.