Previous research found that the duration of segments decreases as children grow older. The development of suprasegmental duration, however, has not been explored. The present study investigated developmental changes in duration of the four Mandarin tones. 5-, 8-, and 12-year-old monolingual Mandarin-speaking children and young adults participated in the study. Tone durations were measured in participants’ production of monosyllabic target words elicited by picture identification tasks. The results were as follows (1) For each tone category, tone duration and variability decreased with age: 5- and 8-year-old children showed significantly longer durations than adults. Tone durations in 12-year-old children approximated adult values. (2) Despite longer durations, adultlike duration patterns across tone categories existed in all children: dipping tones were the longest, followed by rising and level tones, with falling tones being the shortest. (3) Duration differences between the rising and dipping tones became larger as children grew older. The results may be indicative of the general maturation of laryngeal control over age. Although 5- and 8-year-old children have already established lexical contrasts of tone, adultlike phonetic norms are still in the process of development. The developmental data also provide support for a hybrid account of speech production from a suprasegmental perspective.