This paper mainly studies the role of HDAC9‐mediated CaM deacetylation in memory impairment of AD mice, and whether HDAC9‐mediated CaM deacetylation is involved in accumulation of amyloid‐β plaques and tau tangles, neuronal cell death and dendritic spines loss, to be systematically studied in the future. This evidence concerns the gene HDAC9 and Alzheimer disease.