In recent years, the Caspian Sea has become one of the most important strategic areas of the world. However, in spite of its economic potential, the huge exploitation of its reserves along with an increase of the presence of different industrial plants in the sea have caused many problems for its ecology and the environment. The Convention of Tehran to protect the Caspian Sea, as a symbol of regional cooperation, has been adopted by the coastal countries in order to limit the increasing trend of destruction of the sea. Littoral states of the Caspian Sea have ratified this Convention, emphasizing the importance of regional cooperation in saving the Caspian Sea and the necessity of cooperation with related international organizations. This Convention can provide a legal framework to restrict pollution to the Caspian Sea. The fact is that the trend of destruction is faster than the level of environmental cooperation. In this article, by considering the environmental threats for the Caspian Sea, the authors will survey the history and the process of formation of the Tehran Convention. The goal of this article is to identify the capacity of this Convention to decrease the environmental threats to the Caspian Sea.