One of the products of telecommunication technology development is the smartphone. Smartphone using during the Covid-19 pandemic was increased not only in adult users but also in school-age users. Higher user's smartphone in school-age children at risk of causing the addiction. Smartphone addiction does not only cause physical problems but also social, behavioral, and affective aspects. Smartphone addiction can cause depression, neuroticism, and obsessive-compulsive behavior disorders and affect academic achievement. This study is aimed to determine the effect of health education and therapeutic group therapy to prevent smartphone addiction in school-age children. A quasi-experimental research pre-post test with a control group design was used. A total of 69 children were divided into 2 groups. Group intervention 1 consisted of 34 children receiving health education and therapeutic group therapy, assigned to 7 subgroups, whereas group intervention 2 consisted of 35 children receiving only health education and assigned to 7 subgroups. Respondent characteristic data were analyzed using descriptive statistics. The homogeneity of the two groups was tested using Chi-square, a test of the normality of the data using Kolmogorov Smirnov test and data normally distributed, the bivariate analysis using repeated ANOVA. This study found that the decrease in smartphone addiction was greater and significant in the group who received health education and therapeutic group therapy (p-value <0.05). Health education combined with therapeutic group therapy was recommended as an effective nursing intervention to prevent smartphone addiction in school-age children.