In this study it is aimed to analyze the smartphone addiction, fear of missing out (FoMO), and perceived social and academic competence that predict social media addiction on high school students. Study group consists of 296 (136 females and 160 males) high school students studying in Anatolian High Schools and Vocational High School in Mersin during the 2017-2018 academic year. Simple random sampling was used. In the study, descriptive survey method was used. As data collection tools, Personal Information Form, Social Media Addiction Scale, Smartphone Addiction Scale, Fear of Missing Out Scale (FoMO), Perceived Competence Scale developed by Ozer et al. were used. In analyses of data, regression was used. According to stepwise regression analysis, smartphone addiction ([beta] = 0.34), fear of missing out ([beta] = 0.26) and perceived academic competence ([beta] = -0.12) predict social media addiction level on high school students. As the result of the study, smartphone addiction, fear of missing out, and perceived academic competence predict social media addiction on high school students. When the smartphone addiction level and fear of missing out decrease, and also perceived academic competence improve, students' smartphone addiction levels reduce. [This study was presented as an oral presentation at the V. International Eurasian Educational Research Congress (Akdeniz University, Antalya, Turkiye, May 2-5, 2018).]