It has been demonstrated in previous research that the "permeability" of a group boundary influences the members' intention to act collectively as well as their group identity in a subordinate group. In this research, how personal "mobility" of group members affected both in-group collaboration and members' identity was investigated by adopting the "simulated international society game." Each of 344 undergraduates was assigned randomly to one of dominant or subordinate groups with either high or low levels of mobility. Eight games were played in all, and each undergraduate participated in only one of the games. The results indicated that members of both dominant and subordinate groups with low mobility collaborated within their own groups more frequently than those with high mobility. At the same time, members of the subordinate group with low mobility achieved relatively more positive identity than those with high mobility.