The introduction of concept of "Dao" into the Western world can be traced back to the missionary's accounts about Daoism and the Dao folk religion in the 16(superscript th) century. Back then, most of the missionaries, such as Athanasius Kircher, SJ (1601-1680), did not mark the distinction between Daoism and Dao as a religion, and they tended to equate philosophy of Lao-Zi with the heresy of the Dao religion. For them, Daoism and Christianity were completely unrelated or even contrary in their teachings. When Matteo Ricci, SJ (1552-1610) upheld the values and thoughts of the then mainstream Confucianism, Daoism was very much marginalized and neglected by Western scholars. Yet, the situation is reversed after the publication of Confucius Sinarum Philosophus edited by Philipp Couplet, SJ (1622-1693) and his confrères. Though the book could not break the tradition of introducing and discussing the profoundness of Confucianism and Confucius' writings within the theological framework of Christianity, it did provide a brand new way to look at Daoism. Instead of treating it as a religious system, Couplet investigated the philosophical aspect of Daoism and argued that the concept of trinity in Christian thought is embedded in Chapter 42 of Tao Te Ching. The writings of Couplet inspired Joachim Bouvet (1656-1730) and other missionaries in the west to further their studies, which greatly influenced the research of Daoism in the 20(superscript th) Century Europe. This article reconstructs the rise of the missionary sinology in Europe, and discusses the missionaries' interest in Confucianism as well as their understanding of Daoism.