Abstract: The topic of a conversation is the subject or theme of the conversation,and topic transition from the perspective of conversation analysis is understood as a collaboratively constructed social and interactional achievement.Ai in Mandarin is a conversational practice functioning as a topic transition signal.In this study,topic transition is an umbrella term which covers both topic shift and topic change,in accordance with the relationship that exists between the new and previous topics.Furthermore,topic transition is classified as either non-disruptive or disruptive transition in agreement with the sequential position at which a topic transition occurs.Topic transition in two-party Mandarin conversations collected for this study is self-attentive in nature.To compensate for the suddenness of a transition,the interactant implementing the transition might use a free-standing interjection ai as a signal to indicate that a topic transition is about to take place,meanwhile downgrading or even avoiding the suddenness of the transition.