Paul Auster's ethical concerns have never been fully discussed because it is problematic to discuss concurrently his characters' unstable identities as a postmodern feature and their pursuit of responsibility for the other. Introducing the thought of Emmanuel Levinas that postmodern thought and ethics can be compatible, this paper explores Auster's ethical motif from the perspective of alterity, but not from the dialectical choice between the loss or the unity of identity. With specific attention to Levinas's ideas on certain physical dimensions and language, it first argues that the body's passivity constitutes ethical subjectivity in Auster's Moon Palace and finally suggests that "incredible narrative" as a testimony works as an ethical demand in the novel.