The purpose was to explore conditions encouraging to form grand coalition, which leads a group to high solidarity with strong consciousness of intragroup competition. Subjects, 64 male undergraduates, were divided into 16 groups of four persons each. Experiment was carried out with 2×2 design of (consciousness of intergroup competition: strong vs. weak) (consciouness of intragroup competition: strong vs. weak). Results showed that strong competitive spirits against other groups produced facilitative effects on formation of grand coalition even when the consciousness of intragroup competition was strong, and the facilitative effects were strong even when consciousness of intragroup competition was weak. In addition, the necessary conditions for group members to form grand coalition under strong intragroup competition were discussed.