Salicylic acid is widely used for its analgesic, anti-inflammatory, and antipyretic properties, yet its poor water solubility significantly limits its therapeutic applications. To overcome this limitation, a water-soluble phosphorodiamidate prodrug of salicylic acid was developed. The prodrug was synthesized via a phosphoramidation reaction, and its formulation was optimized to enhance solubility while ensuring controlled release. Physicochemical characterization, solubility studies, and in vitro hydrolysis were performed. The prodrug showed greatly improved aqueous solubility and released active salicylic acid gradually in physiological conditions. This approach demonstrates the potential of phosphorodiamidate prodrug design to enhance solubility and delivery of poorly soluble drugs like salicylic acid.