Background <p>In the Kingdom of Saudi Arabia (KSA), adolescent health is suboptimal. Findings reported that 79% of youths aged 15–29 were physically inactive with 30% living with overweight or obesity. Poor dietary habits further complicate the obesity epidemic. Schools are promoted as key settings for obesity prevention, yet little is known about female-only high schools. This study explored barriers and enablers to healthy eating (HE), physical activity (PA), and obesity prevention school-based interventions (SBIs) through conducting focus group discussions (FGDs) with students and staff.</p> Methods <p>Nine FGDs were conducted across three female public high schools in Riyadh from varying deprivation levels; six with 37 students (aged 16–17) and three with 19 staff members. A semi-structured topic guide, informed by the COM-B model, explored capabilities, opportunities, and motivations related to obesity prevention. Framework analysis identified key barriers and enablers to HE, PA, and SBIs implementation.</p> Results <p>Barriers emerged across all COM-B constructs. Capability-related barriers included lack of trained staff. Opportunity-related barriers were most prominent, including hot weather, curriculum limitations, and built school environment. Staff and students collectively agreed that low student motivation was a key barrier. School staff highlighted structural enablers such as the physical education curriculum, while students identified individual-level motivators including willpower, improved mood, health, and body image. No mutual enablers were identified across staff and student groups.</p> Conclusion <p>Female-only high schools in KSA face major barriers to obesity prevention SBIs, with low student motivation emerging as a dominant barrier across staff and student groups. Addressing these barriers through context-specific, multi-level approaches integrating staff and student perspectives is critical for effective SBIs.</p>