INTRODUCTION: Workplace bullying (WB) is a significant occupational hazard for nurses, especially in high-stress environments such as pediatric intensive care units (PICUs). WB adversely affects nurses' physical and mental health, patient safety, and overall quality of care. This study aimed to explore the causes of WB among nurses working in PICUs. METHODS: This qualitative study used a conventional content analysis approach. Eleven nurses from the PICUs of the Children's Medical Center Hospital, affiliated with Tehran University of Medical Sciences, participated in the study. Participants were selected through purposive sampling. Data were collected through semi-structured face-to-face interviews, continuing until data saturation was achieved. The data were analyzed using Graneheim and Lundman's five-step approach. Lincoln and Guba's four criteria-credibility, confirmability, dependability, and transferability-were used to ensure the study's rigor. RESULTS: The analysis of the data revealed two main categories: [1] the "Imposing and Stereotypical Atmosphere," which encompasses sub- categories such as power imbalances, work-related challenges, immature behaviors among staff, and passive reactions of nursing managers
and [2] the "Victim's Achilles' Heel," which emphasizes weaknesses in clinical and communication skills as contributing factors to WB. CONCLUSION: The study identifies organizational and personal factors as causes of WB in PICUs. Nursing leaders can implement targeted interventions aimed at improving workplace culture, monitoring interpersonal relationships, enhancing communication skills, and promoting the clinical skills of staff. These strategies can reduce WB and create a healthier work environment for nurses.