The present study aims to investigate how self-repetition is used to serve communicative purposes in Mandarin mother–child interaction, focusing particularly on mothers’ child-directed speech. The participants of this study consisted of 12 Mandarin-speaking children (4 two-year-olds, 4 three-year-olds, and 4 four-year-olds) and their mothers. Natural conversation from each mother–child dyad was collected for a total of 12 h. The occurrences of self-repetition in the data were analyzed in terms of their forms and functions. The results showed that the mothers of younger children tended to use self-repetition more frequently than the mothers of older children. The predominant form of self-repetition was expanded repetition, and the major functions were soliciting responses and emphasis. Detailed analyses showed how the mothers used the different forms of self-repetition to express various functions. It was concluded that self-repetition in child-directed speech plays an important role in facilitating mother–child interaction and that it may also reflect mothers’ sensitivity to the developing linguistic, cognitive, and communicative abilities of their children.