The aim of the study was to investigate naproxen sodium Eudragit S100 Loaded Nanoparticle. Naproxen sodium is anti-inflammatory Analgesic, Antipyretic drug. There are about seven million patients of rheumatoid arthritis in India. The relevance if RA in India is higher than that reported from China. Indonesia, Philippines and south Africa. Nanotechnology is emerging as promising drug delivery system for twenty first century. Recent studies in field of nanotechnology reveals that vast potential in drug delivery system. The objective of therapy now aims to achieve the low possible levels of disease activity, and reducing of joint damage, enhancing physical function life. Strategies are all aimed at reducing pain and discomfort, preventing deformities and loss of joint function, and maintaining a productive and active life. A sustained release nanoparticle preparation of Naproxen sodium based Eudragit S 100 could retard release of drug which ultimately results in extending pharmacological response of naproxen sodium by reducing frequency of administration, which turns reduces drug related adverse effects. In this study naproxen sodium nanoparticle are prepared to resolve problem of poorly water-soluble drugs.