Aim. This study aimed to investigate the effects of intensive care unit nurses’ personality traits and mentalization on workplace bullying after controlling for organizational culture. Background. Nurses’ personality traits and mentalization may significantly influence workplace bullying. Methods. This cross-sectional study collected data from 416 nurses using an online survey in July 2022. Major variables were evaluated using the Pathological Narcissism Inventory, Perfectionistic Self-Presentation and Psychological Distress Scale, Short Dark Triad, Mentalization Scale, Positive Nursing Organizational Culture Measurement Tool, and the Negative Acts Questionnaire-Revised. . A multiple regression analysis was performed. Results. Narcissistic vulnerability, mentalization, and perfectionistic self-presentation significantly influence workplace bullying (victim aspect). Dark personality, mentalization, and perfectionistic self-presentation significantly influence workplace bullying (perpetrator aspect). Conclusions. Individual nurses could become either victims of bullying or perpetrators according to their personality traits. Therefore, it is necessary to determine their personality traits, so that they do not become influencing factors in workplace bullying. Implications for Nursing Management. Efforts at a nursing organization level are crucial to understand nurses’ personality traits, enhance their mentalization, minimize the manifestations of the negative aspects of their traits, and positively affect the prevention and alleviation of workplace bullying.