Background <p>Metabolic dysfunction-associated steatotic liver disease(MASLD) and diabetes are manifestations of metabolic syndrome. Urinary iodine concentration (UIC) is closely related to diabetes and glucose metabolism, but studies on the relationship between UIC and MASLD in non-diabetic individuals are limited. Our purpose was to explore the associations between UIC and MASLD as well as liver fibrosis in the non-diabetic population.</p> Methods <p>We analyzed data from the National Health and Nutrition Examination Survey (NHANES) conducted from 2017 to 2020. Participants were categorized into three groups based on UIC (µg/L): low (&lt; 100), normal(100–299), and high(≥ 300). Vibration-controlled transient elastography (VCTE) was employed to measure the controlled attenuation parameter (CAP) and liver stiffness measurement (LSM), which serve as indicators of MASLD and liver fibrosis, respectively. Multiple logistic regression was performed to evaluate the association between UIC and MASLD as well as liver fibrosis.</p> Results <p>The study included 1281 non-diabetic participants aged ≥ 20 years. We found that high UIC was associated with a lower MASLD risk (OR = 0.57, 95%CI: 0.37–0.86, <i>P</i> = 0.008) compared to normal UIC. Stratified and sensitivity analyses confirmed these findings. The relationship between log²-UIC and MASLD was non-linear (<i>P</i> = 0.023), with a cutoff value of 84.62&#xa0;µg/L. MASLD risk decreased rapidly when UIC exceeded this value. No significant association between UIC and liver fibrosis was observed.</p> Conclusions <p>In non-diabetic individuals, high UIC is associated with a lower MASLD prevalence, suggesting potential dietary interventions for MASLD patients.</p>