Objective To investigate the correlation of essential hypertension and mild cognitive impairment (MCI) in the elderly. Methods A total of 170 elderly patients with confirmed essential hypertension admitted in our department were enrolled in this study. They were divided into morning blood pressure surge (MBPS) group and non-MBPS group according to the results of ambulatory blood pressure monitoring. Clinical data, such as disease history, blood pressure, body mass index (BMI), fasting blood glucose (FBG), blood lipids, and serum cystatin-C (Cys-C) were collected. Montreal cognitive assessment (MoCA) scale was used to make cognitive assessment. Results There were no significant differences in the age, gender composition, BMI, FBG and blood lipid levels between the 2 groups (P>0.05), but obvious differences of MoCA score and serum Cys-C level were seen (P<0.05). Multivariate regression analysis showed that the Cys-C level was negatively correlated with the MoCA score (OR=2.326, P=0.017), which suggested that serum Cys-C level might be an independent risk factor for MCI in the elderly patients with essential hypertension. Conclusion The serum level of Cys-C in combination with MBPS might be better indicators for assessment of MCI in the elderly patients with essential hypertension.