Background: School students experience problems related to anger and low self- concept that negatively influence their academic and social development and have lasting effects on their well-being. Schools can play a pivotal role in promoting students' mental health and their social, emotional, and behavioural development. Aim: To evaluate the effectiveness of a mindfulness-based intervention on anger and self-concept among preparatory school students. Design: A quasi-experimental design using non-equivalent group designs and preand post-tests were used. Setting: The study was carried out in Salah Salem Preparatory Joint School in Assiut. Sample: A stratified random sample consists of 60 preparatory students. The sample was partitioned into two groups, a study group and a control group (n = 20 students from each grade). Data collection tools: The student's personal data questionnaire, the Adolescent Anger Rating Scale (AARS), and the Beck Youth SelfConcept Inventory scale (BSCI-Y) were implemented. Results: The mean score of the anger scale obtained by the study group was significantly lower than that obtained by the control group in the post-test. Moreover, the mean score of the self-concept scale obtained by the study group was significantly higher than that obtained by the control group in the post-test. Conclusion: The study adds to the growing body of evidence pointing to the contribution of Mindfulness-based intervention efficacy in reducing anger and improve self -concept among preparatory school students. Recommendations: Replication of the study is essential to strengthens confidence in the intervention's effectiveness and ensure generalizability. Empowering the school health nurse to take the lead in implementing the mindfulness program to enhance students' mental well-being is strongly recommended.