Introduction: Chronic diabetes, via reduction of brain neurons, is associated with impaired learning and memory. According to the antioxidant effect of Avicennia marina, this study was conducted with the aim of investigating the neuroprotective effect of aqueous extracts of Avicennia marina on neuronal density in the hippocampal CA1, CA2, CA3, and dentate gyrus in diabetic rats. Materials and Methods: In this study 28 male rats were allocated into equal groups of control, diabetic, and treated diabetic 1 and 2. The diabetes in diabetic and treated diabetic groups was induced using an intraperitoneal (ip) injection of alloxan. The treated diabetic groups 1 and 2 received the aqueous extract of Avicennia marina (ip, 100 and 200 mg/kg, respectively) in alternate days for one month. Sterile distilled water was injected to the animals of control and diabetic groups. At the end of herbal treatments, animals were anesthetized and their brains were removed. After tissue processing, tissue sections were stained with Hematoxylin and Eosin. Then, the neuronal density in the hippocampal CA1, CA2, CA3, and dentate gyrus were investigated. Results: Treatment with Avicennia marina at 200 mg/kg in diabetic rats, but not 100 mg/kg, prevented neuronal loss compared to non-treated diabetic group. Conclusion: Administration of Avicennia marina extract could be protect neurons against diabetes mediated cell degeneration.