BACKGROUND: In South Africa, overweight and obesity affect 17% of children aged 15-18. School food environments play a vital role in children's health, influencing dietary behaviours and resulting in high obesity rates. Interventions targeting schools can contribute to obesity prevention if evidence-based and context-specific. Evidence suggests that current government strategies are inadequate to ensure healthy school food environments. The aim of this study was to identify priority interventions to improve school food environments in urban South Africa using the Behaviour Change Wheel model. METHODS: A three-phased iterative study design was implemented. First, we identified contextual drivers of unhealthy school food environments through a secondary framework analysis of 26 interviews with primary school staff. Transcripts were deductively coded in MAXQDA software using the Behaviour Change Wheel and the Theoretical Domains Framework. Second, to identify evidence-based interventions, we utilised the NOURISHING framework and matched interventions to identified drivers. Third, interventions were prioritised using a Delphi survey administered to stakeholders (n = 38). Consensus for priority interventions was defined as an intervention identified as being 'somewhat' or 'very' important and feasible with a high level of agreement (quartile deviation ≤ 0.5). RESULTS: We identified 31 unique contextual drivers that school staff perceived to limit or facilitate a healthy school food environment. Intervention mapping yielded 21 interventions to improve school food environments; seven were considered important and feasible. Of these, the top priority interventions were to: 1) "regulate what kinds of foods can be sold at schools", 2) "train school staff through workshops and discussions to improve school food environment", and affix 3) "compulsory, child-friendly warning labels on unhealthy foods". CONCLUSION: Prioritising evidence-based, feasible and important interventions underpinned by behaviour change theories is an important step towards enhanced policy making and resource allocation to tackle South Africa's childhood obesity epidemic effectively.