Increasing the number of smartphone users in school-aged children improve the risk of addiction. Children with low self-efficacy tend to use a smartphone as a coping mechanism to create a safe feeling when confronted with an uncomfortable situation or pressure. This study aims to examine the impact of health education and therapeutic group therapy on smartphone addiction and self-efficacy and to investigate the relationship between self-efficacy and smartphone addiction in school-aged children. This study used a quasi-experimental design with a control group. A total of 69 school-aged children were included aged 9-12 years old (10.65 ± 0.785). The respondent was selected with purposive sampling. Intervention group 1 was given health education and therapeutic group therapy, and intervention group 2 was only given health education. Smartphone Addiction Scale (SAS) and Self Efficacy Questionnaire for Children (SEQ-C) were used to measure addiction and self-efficacy. Data were analyzed by using univariate and bivariate. There was a relationship between self-efficacy and smartphone addiction. The decrease in smartphone addiction was higher in intervention group 1, which was given health education and therapeutic group therapy (Mean diff 1.13; 95% CI; 0.052- 2.217). Self-efficacy was also higher in this group (Mean diff 4.46; 95% CI; 6.558- 2.377). Thus, therapeutic group therapy has a significant impact on smartphone addiction and self-efficacy in school-aged children (p-value < 0.05). Self-efficacy prevents children from smartphone addiction. Health education, combined with therapeutic group therapy, is recommended as an effective nursing intervention to prevent smartphone addiction in school children.