---

Malathion is one of the commonest type of organophosphate insecticide whose toxicity in human body is mainly considered to result from the induction of oxidative stress. The aim of this study was to investigate the antioxidant effect of Quercetin, a flavonoid compound, on the spatial memory and oxidative stress parameters during Malathion poisoning in male Wistar rats. This study was performed on nine groups, each of which consisted of eight male rats. Three days after intra-peritoneal injection of Quercetin, Malathion or a combination of these two drugs, the Moris Water-Maze apparatus was used to measure spatial memory parameters. The hippocampus was sampled and the oxidative stress parameters were measured in this area. Intra-peritoneal injection of Malathion (100 and 200 mg/kg) significantly reduced spatial memory parameters (P<0.01) and induced oxidative stress (P<0.001), whereas intra-peritoneal injection of quercetin (50 mg/kg) improved spatial memory in Malathion-poisoned experimental rats (P<0.05). Also, oxidative stress parameters in Malathion-treated groups showed a significant reduction in quercetin treatment (P<0.01). Quercetin was observed to restore the function of spatial memory and the level of oxidative stress parameters of the treated groups with Malathion to the normal level.