Adult hippocampal neurogenesis is closely associated with neuronal plasticity, cognitive function and the etiology of neurological diseases. We previously reported that the standardized ethanolic extract of Prunella vulgaris var. lilacina (EEPV) can be used for the prevention and treatment of cognitive impairments associated with Alzheimer's disease or schizophrenia. In the present study, we investigated the effects of EEPV on cognitive ability in normal naive mice and the underlying mechanism(s) governing these effects, including adult hippocampal neurogenesis. In the passive avoidance task, sub-chronic administration of EEPV (25 or 50 mg/kg, p.o.) for 14 days markedly induced the improvement of cognitive function in mice. In addition, sub-chronic administration of EEPV (25 or 50 mg/kg) for 14 days significantly increased neural cell proliferation and the number of immature neurons, but not newly generated cell survival, in the hippocampal dentate gyrus. Increased ERK, Akt and GSK-3β phosphorylation levels in the hippocampus were also observed after such administration. Our results indicate that EEPV may enhance cognitive function via the activation of various intracellular signaling molecules and the up-regulation of adult hippocampal neurogenesis.