Objective To investigate the effects of the aqueous extracts of ganoderma leucocontextum (GLAE) on cognitive decline of aging rats and possible regulation mechanism.    Methods Fifty rats were divided into five groups, control group, model group, GLAE low-dose group, GLAE middle-dose group and GLAE high-dose group. Aging SD rat models were made by D-galactose, and then treated continuously with different doses (0, 50, 100, 200 mg/kg) of GLAE. The novel object recognition and step down test were performed to detect the changes of rats cognitive function. The brain tissue was stained with toluidine blue, Giemsa and HE staining and observed. The cerebral cell DNA damage was detected by comet assay. Expressions of protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB) signaling pathway related factors in brain were respectively detected by ELISA, Western blotting and Real-time PCR.    Results Compared with the model group, administration of GLAE could obviously alleviate rats cognitive decline and pathological change. The levels of cell DNA damage reduced markedly (P<0.05). The contents of cAMP, brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF), and also expression levels of mRNA and protein of PKA, BDNF, NGF, CREB in the brain increased significantly in each medicated group (P<0.01, P<0.05).   Conclusion GLAE can improve cognitive function, and its mechanism may be related to activation of brain PKA/CREB signaling pathway, increase in neurotrophic factor content and inhibition of cell DNA damage.