Purpose <p>To investigate the correlation between serum uric acid (SUA) levels and the risk for diabetic nephropathy (DN) in Chinese patients with type 1 diabetes mellitus (T1DM) and determine the potential optimal SUA threshold.</p> Methods <p>In this case-control study, 913 T1DM patients were matched 1:1 with healthy controls by age and sex. Multivariable adjusted logistic regression analysis was used to investigate the association between SUA levels and the risk of developing DN. Restricted cubic spline (RCS) was applied to investigate the optimal threshold for SUA. Additionally, longitudinal analysis of 94 patients with at least three visits accessed SUA variability correlations with estimated glomerular filtration rate (eGFR) and urinary albumin creatinine ratio (UACR) changes using Spearman’s correlation analysis. A linear mixed-effects model was performed to access the correlations in SUA, eGFR, and UACR over time.</p> Results <p>T1DM patients exhibited significantly lower median SUA levels (4.24 vs. 4.93&#xa0;mg/dL, <i>P</i> &lt; 0.001) than controls. The incidence of DN was 12% in T1DM patients. After adjusting for confounding factors, the SUA level was inversely significantly correlated with the risk for DN as a continuous variable (OR: 1.47; 1.25–1.74) and in quartile 4 (OR: 3.01; 1.44–6.50), respectively. The RCS plot revealed an identified threshold of SUA as being 4.30&#xa0;mg/dL with increasing risk for DN. Correlation analysis showed the SUA variability significantly correlate with eGFR variability (<i>r</i> = 0.206, <i>P</i> = 0.046) and UACR variability (<i>r</i> = 0.405, <i>P</i> = 0.025). The linear mixed-effects model revealed a significant negative relationship between SUA and eGFR over time (R² = 0.035, <i>P</i> &lt; 0.001), as well as a significant positive relationship between SUA and UACR (R² = 0.041, <i>P</i> &lt; 0.001).</p> Conclusions <p>Our study revealed that decreased SUA level is common in T1DM and identified the threshold as being 4.30&#xa0;mg/dL for increased DN risk.</p>