The growing rates of childhood obesity constitute a public health challenge worldwide. Therefore it is important to identify effective and widely applicable interventions to prevent it. This study aims to explore children’s experience of using a newly developed smartphone application (app) designed to promote healthy eating and evaluate its efficacy on encouraging healthy eating. First, two focus groups were conducted to explore children’s experience of using the app. Then, a quasi-experimental design was used to evaluate the app’s efficacy. The children were asked to use the app for three months. Afterwards, the effect of the intervention was evaluated. 118 children aged 9 to 13 years (M=10.9, Sd=1.1) participated in the study. The children’s experience of using the app was relatively positive, and they found the app easy to use. A significant increase in fruit (η2=.10) and vegetable preferences (η2=.37) and fruit intake (η2=.06) was found in the experimental group. No effects were found for vegetable intake, selfefficacy for healthy eating, or peer norms for healthy and unhealthy eating (p>0.05). The smartphone app-based intervention could potentially serve as an attractive and low-cost intervention to reach a wide population of children for the promotion of healthy eating and prevention of childhood obesity.