Age-related and aged memory deficit changes in Nestin-immunoreactive (Nestin-IR) neurons were studied following recent evidence of distinct Nestin-IR neurons within adult rat basal forebrain. Morris water maze task assessed spatial learning capacity of 3- and 24-month rats (aged-impaired and aged-unimpaired groups). Nestin-IR neuron distributional and morphological features were investigated by immunohistochemistry and positive neuronal number calculation. Nestin-IR neuron number declined with aging, especially aged-impaired. Significant negative correlations existed between average escape latencies and Nestin-IR neuron number in medial septum-diagonal band of Broca (MS-DBB). Correlations of rostral portion [medial septum (MS) and vertical limb diagonal band (vDB)] were higher than caudal portion [horizontal limb diagonal band (hDB)]. Aged-impaired showed reduced complexity of Nestin-IR neuron dendrite arborization and dendritic length. Nestin-IR astrocyte-like cells appeared scattered among Nestin-IR neurons on some aged-impaired slices. In conclusion, aged-impaired rats showed worse cognitive spatial performance and less Nestin-IR neuronal number compared to aged-unimpaired. Nestin-IR neuronal loss and morphological changes are some pathological characteristics of rat aged basal forebrain and may be important in neurobiological mechanisms of brain aging and aged memory deficit.