Social work students experience high levels of stress, which makes them vulnerable to stress-related disorders such as depression. Attachment security has been associated with better stress regulation. Another factor that is closely associated with attachment is mentalization, i.e., the ability to reflect about one's own and others’ mental states, which may also influence the way people cope with stress. The main aim of the study was to investigate the impact of attachment and mentalization on stress, depression, and anxiety in social work students. 460 social work students completed the short version of the "Experiences in Close Relationships-Revised questionnaire” (ECR-RD8), “Relationship Questionnaire” (RQ-2), “Certainty About Mental States Questionnaire” (CAMSQ), “Perceived Stress Scale” (PSS-10) as well as the “Patient Health Questionnaire” (PHQ-9) and the “Generalized Anxiety Disorder Scale” (GAD-7) in a cross-sectional research design. The majority of the current social work students (71.1%) were assigned to an insecure attachment style and reported noticeably high levels of stress, depression, and anxiety. Insecurely attached students showed even higher levels of stress, depression, and anxiety compared to securely attached students. Moreover, the results indicate that securely attached students have better mentalizing skills and that mentalizing skills (partially) mediated the effect of attachment security on perceived stress, depression, and anxiety. Due to the importance of mentalization for stress regulation, mental health, and the quality of relationships, programs promoting mentalization in social work students should be implemented in social work education programs.