A Trademark is a subdivision of  intellectual property law. The legal protection of a sign as a registered trademark requires certain substantive and formal conditions. In this context, distinctiveness is known as the most important substantive requirements for protecting trademark. The distinctiveness means that the sign should be able as a source identifier, and distinguish the products or services to the consumers. The distinctiveness is classified into two types: an inherent distinctiveness, and an  acquiring distinctiveness. The inherent distinctiveness considered distinctive and protected from the beginning of its entry into the market. in acquired distinctiveness, the mark is initially not considered distinctive, but over time, by acquiring, it gains the ability to be registered and protect. However, the important question is: what criteria are used to determine the distinctiveness of a mark, and what criteria can be applied to assess whether a trademark is distinctive?
 The present article concludes that unlike the developed legal systems that have set precise criteria for determining distinctiveness, a legislative gap exists in Iranian law system regarding determination of the types of distinctiveness and and its will be fill legal deficinecies.