The purpose of the dissertation is to examine Mandarin-speaking children's acquisition of a syntax-dependent phonological rule Tone 3 Sandhi (T3S). A Tone 3 (low dipping tone) is changed to a Tone 2 (mid rising tone) when it is followed by another Tone 3. Application of T3S in fact involves a complex process. In setting up the prosodic domains within which T3S applies, syntax is partially referred to. Cyclic and non-cyclic parsing strategies are used for different syntactic contexts. A non-cyclic strategy is used for flat structures (e.g. digit sequences), a cyclic strategy for NPs, and a mixture of both strategies is necessary for sentences. There is also T3S variability because of T3S optional rules. Such variability creates ambiguity in the language input for children. Very little is known about how children acquire T3S. The current work aims to bridge the gap between T3S theories and child language acquisition. This dissertation presents five studies, targeting children's application of T3S in various contexts. Study 1 (Natural speech) examines the production data of seven children (ages 4-6) and their caretakers (five adults). There is T3S variability in children and adults. Study 2 (Flat structures) is an elicited production study participated in by 46 children (3- and 5-year-olds) and 20 adults. We tested the use of a non-cyclic strategy in sequences of two, three, and five digits. The results show that children were able to apply T3S non-cyclically in sequences of digits. However, under-application and over-application are two common error types of children. A surface pattern produced by adults was not found in children. Study 3 (NPs) is also an elicited production study, focusing on the cyclic strategy in NPs, Ninety-four children (ages 3-6) and 20 adults participated in this study. Children were able to apply T3S cyclically in three-syllable compound nouns and four-syllable NPs. However, when the structures become more complex, they may default to the non-cyclic strategy. Study 4 (Natural Speech Repetition) and Study 5 (Robot Talk Repetition) used repetition of sentences to test T3S application at the sentence level where an integration of cyclic and non-cyclic strategies is necessary. Twenty-one children (4- and 6-year-olds) and 11 adults participated in Study 4. Forty-three children (4- and 6-year-olds) and 14 adults participated in Study 5. Children were able to repeat the 4- and 6-syllable sentences which have T3S in Study 4 (Natural Speech Repetition). However, in Study 5 (Robot Talk Repetition) where we used identical sentences, with the removal of the T3S effect, 4-year-olds have a lot of difficulty. Six-year-olds were able to integrate cyclic and non-cyclic strategies in T3S application, but they still do not have adults' mastery of T3S. Six-year-olds have all the T3S patterns adults have, and also approximate adults in their preference of the patterns. Overall, the findings of these studies do not support early acquisition of T3S. The results indicate that although children know to change a Tone 3 to a Tone 2 when it is followed by a Tone 3, it takes time to learn how to set up the prosodic domains for T3S to apply, to develop and reach adult-like mastery of the intricacies of T3S application. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]