One of the ultimate purposes of ecumenical dialogue is to share, beyond mere understanding and reconciliation, special gifts of traditions and spiritual experiences. This paper aims to explore Luther’s doctrine of justification in the ecumenical dialogue, especially investigating “Joint Declaration on the doctrine of Justification”, which is ecumenical document between Lutherans and Roman Catholics. This document says that Lutherans and Roman Catholics has reached a fundamental consensus on the gospel, though they still admitted that even after several years of dialogue they still had differences. The significance of this paper is twofold. First, it will advance Luther research by bringing to light an important ecumenical interpretation and emphasis of Luther’s theology of Justification. It will also contribute to contemporary ecumenical efforts by focusing attention on the dialectic methodology of faith and love in Luther’s theology. In regard to understanding of Luther’s doctrine of Justification in the ecumenical context, this paper suggests two points, which hopes to produce effective results. First, Luther’s teaching should be interpreted in spiritual dimension, that is to say, in terms of mystical union with Christ. Second, it should be understand essential basis of faith for social ethics of Christians. Ultimately, the paper asserts that Luther’s theology of Justification provides underlying principles for Christian ethics today, and that for Luther, faith and love are integrated in his theology.