Aims and objectives: To test the effectiveness of a musical training programme in promoting happiness and quality of life of Hong Kong Chinese underprivileged preschool children. Background: The impact of poverty and income disparity on the psychological wellbeing of children remains a profound global public health concern. There is substantial evidence that poverty and income disparity have many negative impacts on children's psychological well‐being, adversely affecting their quality of life. Methods: A nonequivalent, quasi‐experimental, two‐group, pretest and post‐test, between‐subjects design was conducted with 171 Hong Kong Chinese underprivileged preschool children (aged 3–6 years). Participants (n = 100) in the experimental group attended a weekly 1‐hr musical training lesson for 12 weeks conducted by the Music Children Foundation. Participants (n = 71) in the wait list control group received the same training after all data had been collected. Data collection for both groups was conducted at baseline and 12‐week follow‐up. The measured outcomes were happiness level and quality of life. A TREND checklist was completed. Results: Participants in the experimental group reported significantly higher levels of happiness (p = .002) and quality of life (p = .44) than those in the wait list control group. Conclusions: The present study indicates the effectiveness of a musical training programme in promoting happiness and quality of life of Hong Kong Chinese underprivileged preschool children. It also demonstrated the feasibility of implementing the programme in a community context. Relevance to clinical practice: This study aids to inform nurses the beneficial effect of the musical training programme in improving underprivileged children's psychological well‐being and quality of life. Indeed, community nurses may act as facilitators to promote the musical training programme to underprivileged children. The involvement of community nurses may greatly enhance the sustainability