A recent evaluation of a school nurse-led obesity intervention demonstrated a 5% implementation rate. The purpose of this study was to explore school nurses' perceived barriers to and facilitators of the intervention in order to understand reasons for the low implementation rate. Methods included semi-structured individual interviews with school nurses. Data were analyzed using content analysis and heat mapping. Nineteen nurses participated and eight themes were identified. Parental and administrative gatekeeping, heavy nurse workload, obesogenic environments, and concerns about obesity stigma were barriers to implementation. Teamwork with parents and school staff was a key facilitator of implementation. Nurses also noted the importance of cultural considerations and highlighted the need to tailor the intervention to the unique needs of their school environment and student population. These findings suggest that for school nurses to play a key role in school-based obesity interventions, barriers must be identified and addressed prior to program implementation.