An American-educated liberal and a gentleman in the Western style, Hu Shi characteristically treated his political or intellectual opponents in a fair and graceful manner. But he turned overly harsh and even venomous when dealing with his onetime student Feng Youlan, as well as Feng's works. Scholars have always been intrigued by Hu's Feng Youlan complex. And it appears that even Hu Shi himself was sometimes bewildered about his own attitude toward Feng. This paper systematically examines relevant documents such as diaries, correspondence and manuscripts; attempts to delineate the formation and development of this complex; and sheds light on this dark aspect of Hu's character. It suggests that Hu's Outline of the History of Chinese Philosophy was surpassed and replaced by Feng's History of Chinese Philosophy, and this became a source of annoyance and frustration to Hu.