Observational evidence suggests that increasing fruit and vegetable (FV) intake has the potential to improve children’s cognitive function and mental well-being(1,2), but this has not yet been empirically tested in intervention research. This study assessed the feasibility and acceptability of a multi-component FV intervention, informed by behaviour change science, which measures mental and cognitive health outcomes in children. The ‘Feel Good Study’ was a cluster-randomised wait-list controlled feasibility study conducted in four New Zealand primary schools, with equal allocation of schools to intervention and wait-list control arms. The intervention group received a 10-week FV intervention which included a programme informed by behavioural theory. designed to improve FV availability and acceptance. The wait-list control group received a simplified 5-week version of the intervention. Dietary, cognitive, and mental health outcomes were completed by children and parents/caregivers at the start and end of the 10-week study period. Primary outcomes of this feasibility study were recruitment, retention, and data collection rates. Process evaluation captured measures of intervention fidelity and dose, acceptability, reach, and barriers or facilitators to implementation. Seventy children were recruited (79% recruitment rate), with an average retention rate of 89%. Diet, cognitive, and mental health data collection procedures were feasible, with all data valid for analysis except for 6% of children’s dietary questionnaires. All intervention components were delivered (100% dose delivered), with high levels of fidelity (82% - 100% of components implemented as planned). All teachers and parents strongly agreed that they would recommend other schools/families to take part in the study, indicating high levels of acceptability. The process evaluation revealed areas for refinement, including more cohesive connections between school- and home-based intervention components, enhancing or adding new intervention components, and simplifying enrolment procedures with extended recruitment periods. The key feasibility and acceptance measures in the Feel Good Study were met. We recommend refining the intervention and progression to a definitive trial. This will allow for the first evaluation of the impact of increased FV intake on children’s mental health and cognitive function.