The history of Chinese language is characterized by a clear shift from monosyllabic to disyllabic words (Wang, 1980). This dissertation aims to provide a new diachronic explanation for the rise of disyllables in the history of Chinese and to demonstrate its significance for Modern Chinese prosody and lexicalization. A corpus of 300 Lianmian words in Old Chinese was compiled, including 96 Shuangsheng words, 172 Dieyun words and 32 Splitting-sound words. This study builds on previous morphological and phonological research on disyllables in Chinese and looks closely at detailed aspects of Old Chinese sound patterns and their evolution. Based on the analysis of sound patterns of Splitting-sound words and Dieyun words in Old Chinese, evidence from neighboring languages, statistical analysis of the development of Old Chinese, and reconstructed syllable structure, I argue that the simplification of complex onsets in Old Chinese was a central motivating factor for the rise of the earliest disyllabic forms--Splitting-sound words. Monosyllabic words with historic initial CL clusters (L a liquid), undergo fission, surfacing as disyllables where the first syllable has the simple C onset and the second the L onset. The occurrence of the liquid in the second syllable onset preserves consonant identity, which would otherwise be lost in the onset simplification process. Generalization of this process soon gave rise to another type of mono-morphemic disyllable--Dieyun. Once onset simplification was complete, around Late Old Chinese to Early Middle Chinese period, phonological motivation for syllabic fission disappeared. Mono-morphemic disyllables lost their productivity at this point. The disyllabic template they defined was preserved, giving rise to productive formation of disyllabic compounds. This word-formation process appears to be responsible for the dominance of disyllables in many modern Chinese languages spoken today. This diachronic phonological research accounts for issues that previous studies fail to address. It reveals the relation between the rise of disyllables and the creation of Lianmian words, the relation between the creation of Lianmian words and the simplification of Old Chinese phonology. It enriches our understanding of the role of Lianmian words and of Old Chinese phonological development in Chinese historical disyllabicity. [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.]