In this study we examined the moderating effect of mutual self-disclosure on the self-other mutual influence processes concerning self-appraisal. We hypothesized that the mutual self-disclosure would moderate the identity negotiation processes on the early stage of interpersonal relationship, but on the stable stage it would not. The results consisted with the hypothesis. On the early stage, among the high mutual self-disclosure persons (who perceived that they and a partner had disclosed something about the self each other frequently), the identity negotiation process that self-appraisal was influenced by partner's appraisal was found. But among the low mutual self-disclosure persons (who perceived that they and a partner had not disclosed something about the self each other frequently) the identity negotiation process was not found. On the stable early stage, identity negotiation process was not found regardless of the frequency of mutual self-disclosure. Over all, these results suggest that people negotiate with others on their identity by mutual self-disclosure on the early stage of interpersonal relationships. How the identity negotiation process is conducted on the stable stage was discussed.