This research examined whether there are differences in group decision making between senior leader groups and junior leader groups. Results revealed that senior leaders contributed more during the discussion than junior leaders, and groups with senior leaders performed better than the groups with junior leaders. In post-discussion activities group members noted that senior leaders were able to represent their groups better, and showed better leadership during discussion. On the other hand, the leader's age impacted differently depending on leader selection methods. For senior leaders, leaders randomly assigned were perceived to be more beneficial to groups. However for junior leaders, leaders systematically selected were perceived to represent their groups better and exhibit better leadership. The interaction between leader's age and leader selection seems to arise from a difference of leader's power bases.■ keyword :|Group Decision Making|Leader's Age|Leader Selection|Power Base|