Abstract—Nifedipine, a calcium channel blocker, has been reported to exert pleiotropic effects on atherosclerosis, mainly through its antioxidative properties. However, the effect of the calcium channel blocker on cognitive impairment associated with type 2 diabetes mellitus is not well known. Here, we examined the possibility that a calcium channel blocker could improve cognitive function in a type 2 diabetic mouse model, KK-A^y. KK-A^y mice subjected to 20 trials of a passive avoidance task every week from 7 weeks of age exhibited impairment of the increase in avoidance rate and, moreover, exaggeration of its age-dependent decline, especially after 12 weeks of age. Oral administration of nifedipine at a nonhypotensive dose (0.001% in laboratory chow) to KK-A^y mice from 10 weeks of age improved cognitive function. Nifedipine treatment decreased serum insulin level to one fifth of that in KK-A^y mice without nifedipine. Moreover, nifedipine treatment significantly reduced superoxide anion production in the brain. Furthermore, treatment with nifedipine markedly reduced the mRNA level of Id-1, inhibitor of neural differentiation, in the brain hippocampus. We also observed the increase in blood flow in the brain in KK-A^y mice with nifedipine treatment compared with nontreated mice. Taken together, our findings suggest that nifedipine ameliorates impaired cognitive function in type 2 diabetic mice, at least because of attenuation of hyperinsulinemia and superoxide production in the brain and possible upregulation of the neural differentiation-controlling gene, Id-1.