Background: MiRNAs have emerged as minimally invasive biomarkers with considerable potential for the early detection of oral squamous cell carcinoma (OSCC). Although numerous studies have evaluated circulating miRNAs across different biofluids, the comparative diagnostic performance of saliva-, serum-, and plasma-derived miRNAs has not been systematically clarified. Methods: A meta-analysis was performed by screening PubMed, MEDLINE, Scopus, CINAHL, and related databases. Nineteen eligible studies evaluating miRNA-based assays in saliva, serum, or plasma were included. A random-effects bivariate model was used to calculate pooled sensitivity, specificity, and area under the HSROC curve. Meta-regression using log diagnostic odds ratio (lnDOR) examined whether biofluid type significantly influenced diagnostic performance. Results: Salivary miRNAs showed a pooled sensitivity of 0.76 (95% CI: 0.68–0.82; I2 = 84.69%), specificity of 0.79 (95% CI: 0.70–0.85; I2 = 70.41%), and an AUC of 0.84 (95% CI: 0.80–0.87). Plasma miRNAs produced comparable results with a pooled sensitivity of 0.77 (95% CI: 0.61–0.88; I2 = 90.45%), specificity of 0.79 (95% CI: 0.63–0.89; I2 = 80.20%), and an AUC of 0.85 (95% CI: 0.81–0.89). Serum-derived miRNAs demonstrated the highest accuracy with a pooled sensitivity of 0.82 (95% CI: 0.70–0.90; I2 = 76.92%), specificity of 0.88 (95% CI: 0.75–0.95; I2 = 74.87%), and an AUC of 0.91 (95% CI: 0.89–0.94). Despite serum’s numerically superior performance, meta-regression revealed no significant matrix effect (Wald χ2 = 0.20, p = 0.903). Conclusions: Although serum-derived miRNAs performed best overall, biofluid type was not a statistically significant determinant of diagnostic performance. © 2026 by the authors.