ABSTRACTThe present study sheds light on the contentious relation between religions and prosociality by comparing self-reported altruistic and prosocial behavior among a group of Catholic and Protestant believers. We found that denomination was strongly related to strength of religious beliefs, afterlife beliefs, free-will beliefs, and self-reported prosocial behavior. Denominational differences between Catholics and Protestants in self-reported prosociality were mediated by a stronger endorsement of religious beliefs and belief in predestination but were not related to motivational measures of self-esteem. We also found that the perceived prosociality (i.e., the extent to which others were perceived as being prosocial) was higher for one’s religious ingroup than one’s outgroup, and this effect was stronger for Catholics than Protestants. These novel findings provide an integrated perspective on how religious denominations shape prosocial attitudes and behavior.