Introduction: Trimethyltin (TMT) acts as a potent neurotoxic compound, especially in the hippocampus and therefore, it induces cognitive and memory impairments in both human and animals. The beneficial effects of sodium valproate (VPA) on cognitive functions of the brain havebeen suggested.In the present study, the effect of VPA on learning and memory deficits induced by trimethyltin was investigated in rats using Morris water maze test. Materials and Methods: Twenty three male Wistar rats were divided into control, TMT and TMT+VPA groups. TMT was injected as a single dose (12 mg/kg) in the TMT as well as TMT+VPA groups. Animals of the TMT+VPA group were treated by 10 mg/kg of the VPA daily for 2 weeks. Then, Morris water maze test was performed for all groups. Results: The escape latency and traveled path to reach the platform in the TMT group were significantly higher than control group.Treatment with VPA 10 mg/kg prevented prolongation of escape latency and traveled path induced by TMT application. There were no significant differences between TMT+VPA and control groups. Conclusion: The results of the present study showed that valproic acid prevented TMT-induced memory deficits. Further investigations are needed to elucidate the mechanism of neuroprotective action of VPA in TMT model.