Cognition in all mammals including human beings declines during aging. The cellular events responsible for this decay involve a reduction of neurogenesis in the dentate gyrus. Here, we show that treatment with a nature product from a traditional Chinese medicine, namely salidroside restores the capacity of the dentate gyrus to generate new neurons and intercepts learning and memory decays in mice during aging. We uncover that new neurons in aging mice have functional features of an adult granule neuron by forming excitatory synapses with their putative targeting neurons. Genetic inhibition of synaptic transmission from new neurons abolishes the therapeutic effects of salidroside in behavioral tests. We also identify that salidroside targets CREB transcription for the survival of new neurons in the dentate gyrus of old mice. Thus, salidroside is therapeutically effective against learning and memory decays via stimulation of CREB-dependent functional neurogenesis in aging.