Based on his unsuccessful experience of K2 climbing as a U.S. mountaineering expedition in 1938, the legendary American mountaineer and adventure educator, Paul Petzoldt（ 1908-1999）noted Expedition Behavior （EB） plays an important role in helping expedition members succeed and grow as individuals and as a group. In the field of adventure education, it is considered that EB is an essential educational tool for students to increase their awareness of relationships with themselves, others, the group, and other groups, and that EB enables them to gain the skills to construct a positive community.　In this study, EB of five Japanese college students who participated in the international expedition in the US Rocky Mountains were assessed to understand their experiences of the unique international expedition with consideration of their individual characteristics. In addition, physiological and psychological indications including temperature, SpO2, heart rates, levels of mountain sickness, rates of perceived exertion （RPE）, motivation, anxiety, and feelings were also measured every day in order to understand students’ conditions in the highaltitude mountain environments during the adventure activities.　The descriptive data of EB written by the students during the expedition were analyzed using contents analysis methods, and the results were shown as conceptual diagrams according to the four concepts of EB. In addition, a conceptual diagram was created as an overall summary. Each student’s EB reflected the individual experiences related to personal characteristics, such as personalities, physical strength, motivation, and degree of involvement within the group. Overall, each relationship within the EB framework developed, interacting with personal feelings, physical responses to environments and activities, and group dynamics, and was influenced each other during the expedition. Physiological and psychological indication were also affected by the individual conditions during the expedition.　Overall, the EB of students showed their growths regarding to each relationship within the EB framework, indicating that each of the relationships influenced each other. It was also found that common themes included importance of leadership roles, individual consideration within the expedition team, sharing goals and feelings, communication, and motivation. The results of this study suggest that EB can be a useful educational tool, but it should be recognized that they may be effective only within a careful and secure educational process. It includes students’ preparatory learning about EB, leadership, group dynamics, and basic outdoor skills and experiences, followed by continuous intervention using briefing, debriefing, feedbacking, journaling, and supportive instruction throughout the expedition.