Weak syllables in Germanic and Romance languages have been reported to be challenging for young children, with syllable omission and/or incomplete reduction persisting till age five. In Mandarin Chinese, neutral tone (T0) involves a weak syllable with varied pitch realizations across (preceding) tonal contexts and short duration. The present study examined how and when T0 was acquired by 108 Beijing Mandarin-speaking children (3-5 years) relative to 33 adult controls. Lexicalized (familiar) and non-lexicalized (unfamiliar) T0 words were elicited in different preceding tonal contexts. Unlike previous reports, the present study revealed that children as young as three years have already developed a phonological category for T0, exhibiting contextually conditioned tonal realizations of T0 for both familiar and unfamiliar items. However, mastery of adult-like pitch and duration implementation of T0 is a protracted process not completed until age five. The implications for the acquisition of weak syllables more generally are discussed.