The main subject of this dissertation is Plato's dialectic and the incidental one is the importance of that in the view of Gadamer. This Thesis includes an introduction, four chapters and a conclusion. In the introduction, I write briefly about the background of dialectic from the point of view pre-Socratic philosophers like Zeno of Elea, Protagoras, etc. and about the standpoint of some modern philosophers after Plato such as Kant and Hegel. In the chapter one, I consider Socratic elenchus in the earlier dialogues as a first stage of platonic dialectic that particulars to the public and indicate that maieutic method and anamnesis have a strict linkage. I show also that dialectic is a specific form of dialogue in this stage. In the chapter two, the middle dialogues like Meno, Symposium and specially Republic are discussed and showed that as long as the theory of Ideas becomes important, the theory of king-philosopher gains value and consequently method and science of dialectic become serious. In this stage there are ascending and descending dialectic and philosopher, dialectician and statesman are the same. In the chapter three, the later dialogues such as Sophist, Statesman, Phaedrus and Philebus are under discussion. Plato pursues his argument about dialectic in the form of synoptic method in ascending dialectic and diairetic method in descending dialectic. He insists on the latter than the former. In the last chapter, I talk about platonic dialogue and dialectic used by Gadamer in his philosophical hermeneutics and hermeneutical interpretations of some philosophers like Plato and Aristotle. I insist that the platonic dialectic of Gadamer is hermeneutical not metaphysical and hints at the first stage of platonic dialectic, i.e. Socratic elenchus. In the conclusion, I say that different meanings of dialectic in Plato's dialogues are not separate but they are attached each other in ascending and descending dialectic and therefore we can understand why Plato in Laws and Timaeus returns to the Society and material world