The central question in this article is why the democratic transition that occurred in the former Soviet Union failed to occur in post-Mao China, a question that has rarely been fully stdied in a comparative and systematic way. The first half of the article seeks to solve the methodological problem in comparative research that has limited the ability of social scientists to identify a set of causal variables that shaped contrasting outcomes in the political transition of China ans the Soviet nion. In analyzing regime transitions involving small-n cases, this article adopts the most similar systems design to minimize the problem of causal overdetermination. In so doing, a comprehensive and multi-causal analytical framework of variables is developed and used to formulate a set of hypotheses and explore the causal connections between the key forces and the transition outcome. The second half of the article seeks to provide a systematic, comprehensive, and multi-causal comparison of China and the Soviet Union to capture the shole of the reality of political transition. In contrast to prior studies that have been too narrow to answer the research question, the analysis of the six hypothesized relationships in this article offers an adequate causal explanation for the variation in transition outcome and also makes it possible to predict regime change in post-Deng China.