The Latin manuscript of the "Four Books" in the National Library of Italy is of great academic significance, as it can be dated far earlier than Confucius Sinarum Philosophus in Paris, which was the first complete Latin translation of "Classical Four Books" edited in chief by Philippe Couplet (1623-1693). However, there are different views on the author of the manuscript. Based on textual research on the manuscript and with the help of the research by Italian Sinologist Pasquale M. D'elia, this article further confirms that the author of the manuscript is Michele Ruggieri, the first Jesuit in China. This article also analyzes why the manuscript could not be published timely and thus gives light to the study of the history of spreading of the "Four Books" in the western world.