Background Thyroid stimulating hormones (TSH) are associated with metabolic syndrome (MetS) and share a common pathway with lead in the causation of MetS. Many studies have reported the association of lead exposure and MetS but no study considered the possibility of TSHs working as an intermediate factor in between those two variables. In this study, we examined the role of TSHs as a partial mediator between lead and MetS. Methods A sample of 1,688 adults (≥19 years of age) who participated in the Korea National Health and Nutrition Examination Survey in 2013 was analysed. After adjusting for various demographic and clinical parameters thought of as confounders, the associations between blood lead levels, serum TSH levels and MetS were determined by odds ratios (ORs) obtained from multiple logistic regression models. Results In this study, the prevalence of MetS in the Korean population was 21.9% and the geometric mean of blood lead and serum TSH levels were 1.96 μg/dL and 2.17 µIU/mL respectively. Blood lead was positively associated with high TSH levels (upper 25%) with an OR (95% Confidence Interval (CI)) of 1.79 (1.24, 2.58) per doubling of lead. The increase of blood lead and serum TSH levels both positively increased the odds for the prevalence of MetS. The OR of MetS per doubling of blood lead was 1.53 (1.00, 2.35) and further adjustment for TSHs did not significantly attenuate the OR [1.52 (0.98, 2.34)]. Conclusions These findings suggest that higher levels of blood lead are associated with elevated serum TSH levels and higher risks of MetS. Moreover, by exploring the role of TSH as a partial mediator in the association between lead and MetS, we verified that TSH does not mediate the effect of lead on MetS, therefore confirming that lead has an independent effect on causing MetS.