BackgroundIn the general population, metabolic syndrome (MetS) is associated with increased risk of cognitive impairment, including global and specific cognitive domains. These associations are not well studied in patients undergoing hemodialysis and were the focus of the current investigation.MethodsIn this multicenter cross-sectional study, 5492 adult hemodialysis patients (3351 men; mean age: 54.4 ± 15.2 years) treated in twenty-two dialysis centers of Guizhou, China were included. The Mini-Mental State Examination (MMSE) was utilized to assess mild cognitive impairment (MCI). MetS was diagnosed with abdominal obesity, hypertension, hyperglycemia, and dyslipidemia. Multivariate logistic and linear regression models were used to examine the associations of MetS, its components, and metabolic scores with the risk of MCI. Restricted cubic spline analyses were performed to explore the dose–response associations.ResultsHemodialysis patients had a high prevalence of MetS (62.3%) and MCI (34.3%). MetS was positively associated with MCI risk with adjusted ORs of 1.22 [95% confidence interval (CI) 1.08–1.37,P= 0.001]. Compared to no MetS, adjusted ORs for MCI were 2.03 (95% CI 1.04–3.98) for 22.51 (95% CI 1.28–4.90) for 3, 2.35 (95% CI 1.20–4.62) for 4, and 2.94 (95% CI 1.48–5.84) for 5 components. Metabolic syndrome score, cardiometabolic index, and metabolic syndrome severity score were associated with increased risk of MCI. Further analysis showed that MetS was negatively associated with MMSE score, orientation, registration, recall and language (P< 0.05). Significant interaction effect of sex (Pfor interaction = 0.012) on the MetS-MCI was observed.ConclusionMetabolic syndrome was associated with MCI in hemodialysis patients in a positive dose–response effect.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13098-023-01080-3.