Modernity is not only the basic theoretical horizon of Chinese and Western Marxism, but also their theoretical object. The understanding of modernity has resulted in the respective characteristic Chinese and Western Marxist theories of modernity. These two schools share three epistemological aspects in common: Marxist intellectual origins; the same analytical framework for understanding modernity; and the same understanding of the basic characteristics of modernity. However, they differ greatly from each other in terms of their social backgrounds, basic attitudes towards modernity, and roles in reality. Their common features reveal similarities between all nation-states in world history and the universality of Marxism under specific historical conditions. Their differences reflect the particularities of Chinese and Western paths to modernization, and the diversity of Marxism in the present era. These two Marxist theories of modernity are destined to come into dialogue and be fused into a new Marxist theory of modernity for the 21st century.