This thesis is concerned with the treatment of Catholic themes in 20th -century English novelist Graham Greene's three novels. These are Brighton Rock (1938), The Power and The Glory (1940), and The Heart of The Matter (1948). It examines theological and metaphysical questions that are evoked by these novels, through the help of quotations from these novels. Moreover, this thesis briefly depicts Graham Greene's attitude to Roman Catholicism and religion in general. It also reflects on the thoughts of other writers and scholars who had commented on Greene's Catholic-themed novels. The main questions that are raised in these novels are connected to human damnation and God's mercy.