Background: Non-Alcoholic Fatty Liver Disease (NAFLD) is most commonly associated with metabolic syndrome, but increasing evidence has also implicated environmental toxicants. In this study, we aim to show that elevated blood Lead levels results in worsening liver fibrosis in patients with NAFLD in a large U.S. population-based cohort. Methods: The National Health and Nutritional Examination Survey (NHANES) is a CDC funded nationally representative survey of the civilian United States population. A total of 30,172 patients were included from this survey. 2,499 non-pregnant individuals ages 20-74 were identified with NAFLD as determined by a Fatty Liver Index score ≥ 60 (reference) and included in this study. Advanced fibrosis was defined by the National Fibrosis Score > 0·676. Student’s T-test was used for continuous and Rao-Scott Chi-Square test for categorical variables. Comparison across quartiles was done with simple linear regression for continuous and Rao-Scott Chi-Square test for categorical variables. Demographics and patient confounders were adjusted using multivariate logistic regression (SAS 9·4) for odds of Advanced Fibrosis with respect to Lead quartile. Findings: Increasing blood Lead levels in NAFLD patients is significantly associated with increasing age, male gender, alcohol, smoking, and lower education. After multivariate adjustment for confounding factors, risk of Advanced Fibrosis significantly increased with Lead exposure, OR 5.93, 95% CI 2.88-12.24 in highest Lead quartile (Q4). In subgroup analysis stratified by BMI, a significant association between advanced liver fibrosis and blood Lead levels was consistently present, Q4 (OR 5·78, 95% CI 0·97-33·63) and Q4 (OR 6·04, 95% CI 2·92-12·48) in BMI 30, respectively. Interpretation: Our findings show that advanced liver fibrosis is six times more likely in NAFLD patients with elevated blood lead levels. NAFLD patients at high risk of Lead exposure may need aggressive screening of blood Pb levels to minimize risk of fibrosis progression. Funding Statement: The authors stated: None. Declaration of Interests: The authors declare that there is no conflict of interest or financial support regarding the publication of this paper. Ethics Approval Statement: The datasets generated during and/or analyzed during the current study are publicly available at [https://www.cdc.gov/nchs/nhanes/index.htm].