In the Judaic-Christian tradition, one of the essential problems is how to deal with "eschatology", which means the theory of "last things" in history. Eschatology, therefore, could be understood as an historical point of view, for it has a particular idea that the semantics of "time" derives from the eschatological picture. In other words, eschatology should decide the meaning of the present and direct the process of history. Based upon the above understanding, this essay is an attempt to reinterpret the meaning of "eschatology" in Tillich and through it to think of the relation between "eschatology and ethics". Tillich tries to analyse the notion of eschatology ontologically, since he believes it possible to translate Biblical messages into ontological concepts. In addition, he articulates the significance of existentialism. Tillich is, so to speak, standing on the boundary between ontology and existentialism. This essay consists of four chapters. In chapter I, I propose to summarise the content of Tillich's "Theological Ontology", which shows his fundamental attitude toward "thinking". In chapter II, I consider his "Theological Eschatology", in which Tillich highlights the transcendent end of history. In chapter III, I discuss the ultimate meaning of "Fulfilment of history and Decision", which will indicate "Salvation of history", Finally, in chapter four, I attempt to relate eschatology to "Ethics" by showing that eschatology will require us to make decisions.