<p>This study examines the impact of silicon dioxide nanoparticles (nSiO₂) on the mechanical properties, water absorption (WA), and morphological characteristics of roselle fiber (RF)-reinforced epoxy composites intended for biomedical applications. This is achieved by the implementation of a comprehensive multi-criteria decision-making procedure. The composites were produced by hand layup method with differing weight percentages of nSiO₂ (3%, 6%, and 9%) and RF concentrations (5%, 10%, and 15%). Research demonstrates that the incorporation of up to 6 wt% nSiO₂ increases tensile strength by 35.13%, achieving its maximum at this concentration. The flexural strength increases by 24.24% with 9 wt% nSiO₂, whereas the impact strength achieves its maximum increase of 22.57% with 3 wt% nSiO₂. Water absorption measurements indicate a decrease with higher nSiO₂ concentration and prolonged exposure duration, reflecting improved water resistance. The uniform distribution of nSiO₂ shown by scanning electron microscopy improves water resistance and mechanical properties. The criteria importance through intercriteria correlation (CRITIC) technique were used to provide relative weight to each performance parameter. Composite materials reinforced with nSiO₂ have superior mechanical properties when evaluated by the Measurement of Alternatives and Ranking according to Compromise Solution (MARCOS) methodology. The assessment of the ranking by diverse decision-making tools confirms the validity and effectiveness of the proposed strategy. Optimization assessments utilizing Taguchi and ANOVA corroborate the experimental findings, demonstrating that nSiO₂ enhances composites reinforced with natural fibers. This work demonstrates that nSiO₂ serves as an excellent filler for green composites, enhancing their mechanical properties and moisture resistance.</p>