Knowledge has been recognized as an important resource that should be carefully managed in order to enhance organizational competitiveness. Therefore, it is important to manage knowledge resources that have been learned and stored in organizations. Several scholars in the public administration literature have examined whether public service motivation (PSM) can help employees share their knowledge in ways that contribute to the effective functioning of public organizations. However, the mechanisms by which PSM influences individuals’ propensity to share knowledge have not been clarified by past research. Against this background, at first, this study contributes to understanding the relationship between PSM and knowledge sharing by applying self-determination theory with a logical insight of the intrinsic knowledge sharing motivation process. This study also examined that relationship by testing three competing psychological mechanisms based on person-environment (P-E) fit theory: (1) person-group (P-G) fit, (2) person-job (P-J) fit, and (3) person-supervisor (P-S) fit. The research questions for this study are as follows: Do individuals with higher levels of PSM have a higher propensity toward knowledge sharing? Does the congruence between employees and their work environment increase employees’ knowledge sharing behavior? Do PSM-driven employees have higher willingness to fit in the work environment? Does P-E fit theory help explain the causal relationship between PSM and knowledge sharing? Based on primary data of 1,094 occupationally diverse employees working in 33 local governments in South Korea, the current study found that caution should be exercised when making claims regarding the effects of PSM on individuals’ propensity to share knowledge and that greater emphasis should be placed on ways public sector organizations can foster P-G fit and P-J fit. However, this study also found that the relationship between PSM and knowledge sharing is not mediated by the extent to which employees perceive that their values are congruent with those of their supervisors. Keywords: public service motivation (PSM), person-environment fit (P-E fit), person-group fit (P-G fit), person-job fit (P-J fit), person-supervisor fit (P-S fit), knowledge sharing