The present study aimed to examine a structural equation model of smartphone addiction based on the roles of anxiety and depression, with metacognition as a mediating variable, among male adolescent students. This research employed a descriptive–correlational design, and the statistical population consisted of male students in District 1 of Karaj during the 2023–2024 academic year. A total of 361 participants were selected through random sampling. Data were collected using the Metacognition Questionnaire by Wells and Cartwright-Hatton (2004), the DASS-21 by Lovibond (1995), and the Smartphone Addiction Scale (SAS) developed by Kwon et al. (2013). Pearson correlation analysis and structural equation modeling were used to analyze the data. Findings indicated that the proposed model demonstrated a satisfactory fit among the adolescent participants. Results further showed that anxiety (β = 0.42, p < 0.01), depression (β = 0.11, p < 0.01), and metacognition (β = 0.40, p < 0.01) each had a direct and positive effect on smartphone addiction. These outcomes suggest that psychological interventions grounded in metacognitive approaches may effectively reduce dependence on modern digital technologies and support healthier behavioral patterns during adolescence.