This paper considers how James Joyce criticizes the Irish Catholic Church through Leopold Bloom in his novel Ulysses. Joyce regards England and Rome (the Catholic Church) as dominant powers that have oppressed individuals for a long time. The Church has suppressed and had great influence on the life of the people in Ireland. Joyce uses Bloom to criticize the problems of the Church. Bloom exists on the border of the Dublin community, which enables him to defamiliarize the dogmas of the Catholic Church. Because of his complicated identity, Bloom is isolated from the mainstream society of Dublin, but his status permits him to view it with a critical eye. His impartial observation discloses the Catholic Church’s aggressive, imperialistic, and commercial features that lie behind the missionary work. Compared to its aggressive missionary work, the Church shows little interest in the economic distress of its families. The Church also controls the people with confession and penitence, and paralyzes the people by giving “cold comfort”. This paper affirms that Joyce reveals these negative aspects of the Irish Catholic Church through Bloom, his “useful weapon.”