Objective: To explore the relationship of the level of 25 hydroxyvitamin D [25(OH)D] with the degree of neurological deficit and post-stroke cognitive impairment (PSCI) in elderly patients with cerebral infarction. Methods: A total of 120 elderly patients with cerebral infarction were admitted to our hospital from June 2019 to December 2020 were selected. The degree of neurological deficit was assessed by National Institutes of Health Stroke Scale (NIHSS), and the cognitive function was assessed by Montreal Cognitive Assessment (MoCA). According to the level of serum 25(OH)D, the patients were divided into a vitamin D normal group (≥20 ng/mL, n=46) and a vitamin D deficiency group (<20 ng/mL, n=74). The clinical characteristics of the two groups were compared, the relationship of serum 25(OH)D level with NIHSS and MoCA scores was analyzed, and the influencing factors of PSCI were analyzed by multivariate logistic regression model. Results: The NIHSS score, incidence of PSCI, LDL-C and HbA1c in vitamin D deficiency group were higher than those in the vitamin D normal group, while MoCA score and HDL-C were lower than those in the vitamin D normal group (P<0.05); serum 25(OH)D level was negatively correlated with NIHSS score (r=−0.723, P<0.05), and positively correlated with MoCA score (r=0.668, P<0.05). The incidence of PSCI in elderly patients with cerebral infarction was 35.83% (43/120). Logistic regression analysis showed that age, history of hypertension, drinking history, NIHSS score, 25(OH)D, and LDL-C water were the independent influencing factors of PSCI (P<0.05). Conclusion: The level of serum 25(OH)D in elderly patients with cerebral infarction is closely related to the degree of neurological deficit and cognitive function. Lower 25(OH)D level increases the risk of PSCI.