Nimodipine might be effective in subcortical vascular dementia(VaD). Its benefit in preventing further cognitive decline in patients with acute ischemic stroke(AIS) and vascular mild cognitive impairment(VaMCI) remains to be established. In this multicenter, double-blind trial, we randomly assigned 654 eligible patients to nimodipine 30 mg three times a day or placebo. The primary outcome was any cognitive decline defined by the changes on the Mini-Mental State Examination(DMMSE à3) or vascular AD assessment scale cognitive subscale(DADAS-cog ! 4) at 6 months. Secondary outcomes included any distribution shift of DADAS-cog, DMMSE or cognitive improvement defined by DADAS-cog à2, or DMMSE ! 0. The primary outcome in the nimodipine group and placebo group were similar for DMMSE à3(4.18% and 7.22%, respectively, P = 0.15) and DADAS-cog ! 4(8.36% and 8.93% respectively,P = 0.88). The distribution shift of DADAS-cog and DMMSE differed significantly between the two groups(P = 0.03 and P = 0.05 respectively). Cognitive improvement occurred in 55.4% in the nimodipine group and 43.6% in the placebo group measured by DADAS-cog à2(Odds Ratio, 1.54; 95% confidence interval[CI] 1.10–2.14, P < 0.01) or 84.0% and 74.6% respectively by DMMSE ! 0(Odds Ratio, 1.79; 95% CI 1.18–2.70, P < 0.01). Nimodipine was associated with better cognitive function in the memory domain. The adverse events rate was similar in two groups. This study is registered with ClinicalTrials.gov,NCT01220622. Nimodipine did not show benefit to prevent cognitive decline in AIS patients with VaMCI, but improved cognition moderately, especially measured in the memory domain.