Tasks with different design factors may dissimilarly affect oral production, and thus can be adopted for different pedagogical purposes. However, the functions of task types are not fully explored. To address this gap, this study investigates the influence of content familiarity and task repetition on sixty English as a foreign language learners’ speaking performance, in terms of complexity, accuracy, and fluency (CAF). Participants twice performed four monologic tasks, and received stimulated recall interviews. The findings indicate that participants produced structurally more complex speech under familiar conditions, and increased their CAF in task repetition. Furthermore, content familiarity and task repetition may facilitate conceptualization. Task repetition may also direct participants’ attention towards lexical choices and grammatical encoding. Moreover, repeating unfamiliar topics effectively increased CAF. The findings suggest content familiarity and task repetition are two dimensions of topic familiarity, and that teachers might consider implementing task repetition when presenting unfamiliar topics to learners.