This case study investigated the changes of four Korean English major college students’ motivation and interest in TOEIC studying based on qualitative research method. Semi-structured interviews were conducted once a month for six months. Interest is a unique motivational variable with affective and cognitive domains together including interactions between persons and their objects wheres motivation is more broad, psychological and overlapping concept compared with interest. The results showed that the participants expressed the strong instrumental and extrinsic motivation for TOEIC studying while they confessed the intrinsic motivation for English learning. However, some participants had both extrinsic and intrinsic motivation on TOEIC studying as time went by. The participants’ strong perceptions on TOEIC in Korea were strongly related with situational interest in TOEIC or TOEIC studying. The participants’ interest in TOEIC studying was triggered as they improved the TOEIC score. However, one participant showed the expiration of interest in TOEIC studying right after achieving a high TOEIC score, but his interest in potential English studying was triggered.