This paper aims at examining Doctor Sloper’s contradictory duality in Henry James’ Washington Square. James effectively portrays his inner figure through the use of irony and conveys the spirit of American society. This novel deals with the relationships and conflicts of Doctor Sloper, Catherine and Morris Townsend. Doctor Sloper is the important character who has a scholarly doctor with his learning and skill and is proud of his perfect life. He notices that Morris tries to entice his daughter for the purpose of having her money. And he opposes her marriage with Morris because of his incapacity for money and his snobbery. His opposition shows that he performs parental duty to protect his daughter. But there is another psychological factor to work. It is his hidden inward disposition, that is, the secular and material propensity. After Doctor Sloper finds this from Morris, he tries to deny his own material disposition through his loathing about Morris. It means that he projects Morris the shadow of his own ego and hates him. But Morris’ appearance brings about the contradiction between Doctor Sloper’s perfect image and his reality and there occurs his irony. Therefore, the essence of irony from the Doctor himself and from the extreme relationship between him and Morris can be fully understood through in-depth and internal analysis of characters.