This study investigates the developmental trajectory of relative clauses (RCs) in Mandarin-learning children's speech. We analyze the spontaneous production of RCs by four monolingual Mandarin-learning children (0;11 to 3;5) and their input from a longitudinal naturalistic speech corpus (Min, 1994). The results reveal that in terms of the syntactic role of the head noun in the matrix clause, isolated noun phrase RCs dominate, followed by those that modify the subject or object of the matrix clauses and predicate nominal relatives. This pattern differs from those observed in English (Diessel & Tomasello, 2000), German (Brandt, Diessel & Tomasello, 2008), and Japanese (Ozeki & Shirai, 2007). Regarding the syntactic role of the head noun inside the RC (i.e. subject, object, or oblique relatives), the early RCs are dominated by object relatives. This pattern also differs from those observed in English and Japanese. We propose a multifactorial usage-based learning account for the developmental patterns.