Considering the dynamicnature of foreign language anxiety (FLA), we applied an idiodynamic method to explore topic-based variations of FLA. Before the study was conducted, a class of 20 female intermediate English as foreign language learners were assessed using the foreign language classroom anxiety scale (FLCAS). Two low-anxiety learners and two high-anxiety learners were selected to participate in this study. The idiodynamic method involved videotaping the participants’ responses to four topic-based questions, their self-ratings of fluctuations in FLA while answering the questions, and drawing attributions for topic-based changes in FLA. The results demonstrated both within-individual and between-individual stability and variation in FLA. Linguistic block, topic familiarity, topic interest, and topic-related emotional loading were revealed as the major factors affecting the dynamics of FLA. The pedagogical implications of the findings are discussed.