BACKGROUND: There is a paucity of prior research on residual cholesterol (RC) and hyperuricemia, and it remains unclear whether body mass index (BMI) functions as a mediating factor between them or intensifies lipid metabolic dysregulation, thereby elevating the risk of hyperuricemia. This study aims to investigate whether BMI mediates the association between RC and hyperuricemia, as well as the interaction or joint effect of BMI and RC on hyperuricemia. METHODS: This is a cross-sectional study, involving a total of 14,218 hypertensive patients. Exposure factors include RC and BMI. The outcome was Hyperuricemia, defined as serum uric acid (SUA) ≥ 420 µmol/L. Multivariable logistic regression models and causal mediation analysis were used to examine the association between RC and BMI and the prevalence of hyperuricemia. RESULTS: A total of 14,218 hypertensive patients were enrolled in this cross-sectional study, comprising 6,713 (47.2%) males, with a mean age of 63.8 (9.36) years. The prevalence of diabetes mellitus was found to be 10.4% (1,473), while hyperuricemia accounted for approximately 44.4% (6,319). The results show that there is a linear positive correlation between RC and hyperuricemia (P for trend < 0.01). RC and BMI only had significant additive interaction on hyperuricemia, but there was no multiplicative interaction (Additive: RERI = 0.45, 95%CI: 0.13-0.78; Multiplicative, OR = 1.09, 95% CI 0.92-1.3, P = 0.308). There are direct and indirect effects between RC and hyperuricemia [estimate (95% CI): DE = 0.063 (0.048, 0.070), IE = 0.005 (0.003, 0.001)]. In the aforementioned causal mediation analysis, among the hyperuricemia caused by RC, BMI mediates 7.1%. CONCLUSION: The intermediary role of BMI and its interaction with RC play a pivotal role in augmenting the prevalence of hyperuricemia. TRIAL REGISTRATION: Registered prospectively in the Chinese Clinical Trial Registry (ChiCTR1800017274) on July 20, 2018. Access at https://www.chictr.org.cn/showproj.html?proj=28262 .