This investigation delves into combined alkali plus silane treatment. The research looks into its effects on the properties of Cryptostegia grandiflora (CG) fibers. These fibers are utilized in biomedical applications. The combined NaOH and silane treatment increases the hemicellulose content while decreasing the cellulose content, with the degree of cellulose reduction dependent on the concentration and duration of the treatment. The crystallinity index of the treated fibers decreases by 25–34% compared to untreated, NaOH and silane treated fibers, leading to a 22–38% reduction in tensile strength. However, the treatment enhances thermal stability, with the fibers exhibiting a significant residue at 550 °C. The surface morphology of fibers under treatment is diverse. We see a cleaned smoothed or roughened surface. This can improve interfacial bonding with resin. It also enhances the mechanical properties of composites. The treatment of fibers is complex. It results in a variety of surface appearances. These will improve the fiber-resin bond. And overall strengthen the mechanical properties of resulting composites. The optical properties of Cryptostegia Grandiflora fiber, influenced by combined alkali and silane treatment, are critical for optimizing its performance in biomedical applications.