This dissertation studies the realization of the rhythm of Taiwan Mandarin and focuses on the quality of its unstressed (neutral-tone) syllables. Taiwan Mandarin (TM) is often described as more syllable-timed than Standard Mandarin (SM). In TM, the unstressed syllables occur less frequently. The quality of the unstressed (neutral-tone) syllables in TM also seems to differ from those of SM. The results show that most of the neutral-tone syllables have a mid-low pitch target except in some frequent vocabulary items, or when the original lexical tone is obvious. Unlike SM, the neutral-tone syllables of TM do not undergo tone loss. The neutral tone in TM has a mid-low pitch target in disyllabic words, neutral-tone sequences and novel formations. The pitch target of the neutral-tone syllables is generally not as low as the low tone, and the carry-over effect of the preceding tone is stronger in the neutral tone than in the low tone. Also, there is no general syllable reduction in the neutral-tone syllables in TM. The durations are shorter than their full-tone counterparts only when their rimes are [[schwa]] or [[barred-i]], and the duration differences are much smaller than in SM. The results suggest that these syllables are better characterized as having a lexical tone, which can be considered the fifth tone in the language. SM, in contrast, has four lexical tones. The perception tests further show that TM listeners rely on duration, pitch, and vowel/voice quality to distinguish the low tone from the innovative fifth tone. Specifically, for the pitch cues, they rely on low end pitch and fast-falling pitch contour to identify the low tone. The results also show that the perceptual distinctions made by the TM speakers between the low tone and the fifth tone were very weak. The TM listeners could only distinguish 20% of the unaltered pairs. Along with the evidence found in the production tests, this study finds that the innovative fifth tone is on the verge of merging with the low tone. [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.]