Extending the common ingroup identity model (Gaertner et al. 1993, European Reveiw of Social Psycology, Vol. 4, pp. 1-26) and social categorization theory (Turner et al. 1987, Rediscovering the Social Group: A Self-Categorization Theory, Oxford: Basil Blackwell.), the current study investigates when superordinate categorization with an opponent occurs during intra- and intercultural integrative negotiation. I hypothesize that a high level of interdependent self-construal (Markus and Kitayama 1991, Psychological Review, 98, 224-253) is associated with early superordinate categorization with an opponent and favorable judgment of an opponents cultural group before negotiation takes place, whereas a low level of interdependent self-construal shows favorable judgment of an ingroup and outgroup after negotiation is closed. One hundred fourteen participants of the U.S. and the Republic of Korea completed a multi-issue negotiation simulation with integrative potential in either intracultural or intercultural dyads. Results support the hypotheses. I discuss theoretical and practical implications of the sensitivity of interdependent self-construal to social context and fluid boundaries of ingroups and outgroups, and the role of integrative negotiation in improving intergroup relations in globalizing and multicultural organizations and societies.