Smartphone has become highly prevalent in recent years. It demonstrates as a useful technology that brings productivity and convenience in our daily life. However, smartphone usage can also drive psychological and behavioral maladaptive dependency, which may result in negative problems. Given that research on smartphone addiction is still limited in the information systems literature, this paper aims to propose a framework of motives from the functionalist perspective and investigate why users will be addicted to smartphones. Four categories of motives for smartphone usage are proposed in this study. They include enhancement motives (i.e., information seeking and perceived enjoyment), social motives (i.e., social relationship), coping motives (i.e., mood regulation and pastime), and conformity motives (i.e., conformity). We empirically test our research model using online survey method. The findings illustrate that perceived enjoyment, mood regulation, pastime, and conformity positively affect smartphone addiction, whereas information seeking and social relationship have no significant effects. Implications for both research and practice are provided.