The Theory of Ideas suggested by Plato has had a great impact on different fields of philosophical discussion because it suggests a wider universe including being with a distinctive feature. Shaykh Ishraq, Shahabuddin Suhrawardi sympathized with this theory. He gives a determining place to "ideas" in his ontological system and tries to establish it through firm arguments. He also makes all his efforts to give this theory a more plausible and more rational structure by explaining the relation of the world of ideas with its superior and inferior worlds.This article is an inquiry into the definition and nature of ideas from the viewpoint of Plato and Shaykh Ishraq, the latter's arguments for establishing such a world, and the place of this theory in the ontological system of the two thinkers. The main objective of the author, however, has been to investigate about Suhrawardi's point of view; therefore, Plato's theory has been discussed in order to show the commonalities and the differences between the two theories.