Objective To investigate both the role of apoptosis in the pathogenesis of amyloid β-peptide1-40 (Aβ1-40) and the therapeutic effect of Prepared Radix Rehmanniae (PRR) on the neurotoxicity of Aβ1-40 in rat brains. Methods A 5 μL volume of Aβ1-40 or vehicle was injected into the left lateral ventricle to establish an animal model with Alzheimer's-like disease. Morris water maze tests were used for behavioral study. Western blot and kinase activity assess were used to determine the expression and activity of caspase-3 in the hippocampus. The hippocampal neuronal apoptosis was observed by DNA electrophoresis. Aβ1-40 injected rats were treated with PRR at a large or small dose for 21 consecutive days. Results Intracerebroventricular injection of Aβ1-40 induced a marked learning and memory dysfunction in Morris water maze tests. Apoptotic changes were detected in the hippocampus of Aβ1-40 injected rats, such as the increases of the concentration and activity of caspase-3, nucleus degeneration. After treatment with PRR [8, 4 g/(kg·d), ig], the changes mentioned above were significantly improved. Conclusion Aβ1-40 could induce hippocampal neuronal apoptosis. PRR can remarkably inhibit the neuronal apoptosis. This may be one of the therapeutic mechanisms of PRR improving the impaired learning and memory induced by Aβ1-40 in rats.