The introduction of Western philosophy and theology into China by the Jesuits during the seventeenth-century constituted the first philosophic and religious dialogue between China and Europe. The philosophic content of Jesuits' writings on this subject has not yet been explored in depth. This article focuses on the translation of the concept "substantia" which derives from the term "ousia" used in Aristotle's philosophy. It analyses the etymology of the term and its usage in Greek philosophy. It then considers the translation of ousia into Latin and its transformation in Christian theology. Afterwards, it discusses two Chinese translations of this term in the Tianzhu shiyi by Matteo Ricci and the Mingli Tan by Francisco Furtado and Li Zhizao, thereby uncovering the connotations of the Chinese words chosen by the translators and the underlying problems of comparative philosophy. While the translation of "substantia" reflects the strategy of accommodation adopted by the Jesuits, it also reveals the differences between Chinese philosophy and Western philosophy.