Information system introduction is an organizational learning process, in which organizational members learn how to introduce information system into an enterprise. While learning, however, individuals always act defensively ¡XModel I theories-in-use, and the defensive behaviors usually bring counterproductive or unintended consequences or limited learning (Argyris, 1978, 1985, 1990, 1999). Similarly, in the process of introducing information system, the organizational members' defensive behaviors will make information system cannot completely meet the business needs or cause schedule delay. In this research, we conduct a case study to explore the defensive phenomenon during the process of introducing information system. Based on theories of action and literature about organizational defense (Salaway, 1984, 1987; Wastell, 1999; Henfridsson & Soderholm, 2000), we investigate the defensive phenomenon and generalized it into ten stories. The analyzing results show that users, MIS staff, and top managers all have defensive behaviors in introducing information system and thus cause negative effect. Therefore, this research suggests the organizational members move from Model I to Model II orientation and practice to introduce information system more effectively.