Public Service Motivation (PSM) is a topic that has generated considerable interest among Public Administration scholars. Research on PSM has mainly focused on either defining what PSM is and how this construct can be measured or on testing how PSM affects individual and organizational variables. However, very little is known about how the motivation to serve the public interest is influenced by personality. We evaluate the psychological antecedents of PSM by distinguishing two classes of motives behind PSM: affective versus nonaffective motives. Our analysis of data from responses to two independent questionnaires by 320 undergraduate students reveals that PSM is strongly influenced by core personality traits. Our results suggest that affective motives of PSM—Compassion (COM) and Self-Sacrifice (SS)—are positively influenced by the personality traits of Honesty-Humility, Emotionality, and Agreeableness, and negatively by Conscientiousness. In contrast, nonaffective PSM motives—Attraction to Policy-Making (APM) and Commitment to the Public Interest (CPI)—are positively associated with the Openness to Experience trait.