ToyBox Study Malaysia (TSM) is an evidence-based programme aimed at preventing childhood obesity by promoting healthy behaviours among preschool children, including water consumption, healthy snacking, increased physical activity, and reduced sedentary time. Adapted from ToyBox Study Europe, TSM was first implemented in Malaysian preschools in 2018 and later converted into an online learning system, eToyBox. This study evaluated the effectiveness of eToyBox compared to print-based learning in enhancing preschool teachers’ knowledge, attitudes, and self-efficacy in teaching these behaviours. This cluster-randomized controlled study involved 138 preschool teachers assigned to control group (CG), intervention group I (IG-I), or intervention group II (IG-II). IG-I ( = 46) completed 13-week asynchronous eToyBox programme, while IG-II ( = 47) implemented printed ToyBox modules over the same period. CG received no intervention but completed the same assessments. Outcomes were measured using ToyBox Teacher’s Questionnaire at baseline (T0), post-intervention (T1), and 3-month follow-up (T2), and analysed using Friedman test and repeated measures ANOVA. Compared to CG, IG-I teachers showed significant improvements in knowledge, attitudes, and self-efficacy after eToyBox programme (