The purposes of this study were to identify the process of becoming a fan of a professional baseball team and to examine the transformation of fans' attitudes by using the longitudinal interview method. The interviews of five fans of the Osaka Kintetsu Buffaloes were conducted from August 27^<th> to September 5^<th>, 2005 (first interview)and from November 9^<th> to December 2^<nd>, 2005 (second interview). The results of the interviews indicated that the primary factors of becoming a fan of the team were location, game attendance experience, players interest, reference group and the allegiance of other family members. Furthermore, the results showed that the attitudes of fans toward the team wavered during, before, and after the bankruptcy of the Osaka Kintetsu Buffaloes.