Generally, one of the most important impediments before persons who wants One of the most important obstacles faced by those who intend to enter the inventions market is the concern about violation of others rights, which usually will result in severe sanctions in legal systems. In this situation, those Persons need a solution, which give them the opportunity, before start investment, to ask the court if their acts are violation of a patent right. In U.S.A law, this solution afforded by declaratory judgment. In Iran law, although article 18 of patents, industrial designs and trademarks act permit any interested person to ask invalidity of a patent, but by court’s limited interpretation of the notion of interest, acceptance of these actions is in uncertainty. Declaratory judgment, by interpretation of patent’s vague claims and checking of its validity, by removing of any uncertainty about patent infringement and deletion of non-proper patents, will be helpful in the process of research and improvement of innovation and support pubic knowledge.