Objectives: This study investigated the role of internalized shame as a mediator in the relationship between perfectionism and non-suicidal self-injury (NSSI), and examined whether this mediated relationship is moderated by distress tolerance. Methods: A sample of 408 university students completed measures assessing NSSI, perfectionism, internalized shame, and distress tolerance. Data from 216 participants (mean age = 22.18 years, 69.4% female) who reported experiencing NSSI in the past year (i.e., in 2022) were analyzed. Results: The results indicated that internalized shame mediated the relationship between functional-dysfunctional perfectionism and NSSI. Furthermore, distress tolerance moderated the relationship between internalized shame and NSSI. Finally, the mediating effect of internalized shame in the relationship between functional-dysfunctional perfectionism and NSSI was also moderated by distress tolerance. Conclusions: These findings suggest that perfectionism contributes to NSSI through internalized shame, with distress tolerance acting as a protective factor. This study highlights the importance of addressing both internalized shame and pain tolerance in interventions targeting individuals at risk of NSSI owing to high levels of perfectionism. Keywords: NSSI (non-suicidal self-injury), perfectionism, internalized shame, distress tolerance