This study investigated the effects of gender membership salience on individuals' selfdefinition, self-concept, evaluation of others, and selection of people as their group members. They were assigned to one of two discussion topics which consisted of two males and two females; 'the reason why women cannot be promoted to be a manager' or 'improvement of the Orientation Camp'. Gender were more salient in the former topic, and less salient in the latter topic. According to social identity theory, high gender salient group members would mention more their gender in spontaneous responses to the question 'Who am I', define themselves more gender stereotypically, and exibit ingroup bias in evaluation of others than low gender salient groups. The result about self-definition supported the social identity theory. In high gender salient groups, men defined themselvs more masculine and women defined themselvs less masculine or more feminine than in low salient groups. Especially men and women with traditional attitude toward sex-roles defined themselves more stereotypically than non-traditionals. In self-definition, women used gender-schema (Bem, 1985) and men used group-schema (Markus, et. al, 1982) regardless of gender salience level. Ingroup bias in evaliation of others were exibited by women but not by men regardless of gender salience level.