BACKGROUND Metabolic syndrome (MetS) is related to poor cognitive function. However, the results of previous studies were inconsistent, and whether the ApoEε4 allele modifies the association remains unclear. AIM To elucidate the relationships among MetS, ApoEε4, and cognitive dysfunction in an elderly population in China. METHODS One hundred elderly patients with MetS and 102 age- and gender-matched controls were included in the study. Baseline clinical characteristics and biochemical index for glucose and lipid metabolism were obtained. The distribution of ApoEε4 was assessed with PCR restriction fragment length polymorphism analysis. Cognitive function was evaluated by mini-mental status examination at the 1-year follow-up examination. RESULTS Compared with controls, MetS patients had worse cognitive function and decreased ability to participate in activities of daily life (P = 0.001 and 0.046, respectively). Patients with cognitive dysfunction had higher prevalence of MetS (62.1% vs 36.4%, P < 0.001) and were more likely to carry the ApoEε4 allele (22.3% vs 10.1%, P = 0.019). Multivariate logistic regression analyses showed that diagnosis with MetS, severe insulin resistance, status as an ApoEε4 carrier, higher systolic blood pressure, and larger waist circumference were risk factors for cognitive dysfunction (P < 0.05). Repeated-measures analysis of variance, performed with data collected at the 1-year follow-up, revealed continuous influences of MetS and ApoEε4 on the deterioration of cognitive function (time × team, P < 0.001 for both) CONCLUSION Diagnosis of MetS and ApoEe4 carrier status were persistently associated with cognitive dysfunction among an elderly population in China. ©The Author(s) 2021. Published by Baishideng Publishing Group Inc. All rights reserved.