Background. The relationship between smartphone addiction (SPA) and loneliness is examined in several studies, however, the mediating effects of the variables related to narcissism and the family on the relationship between SPA and loneliness are not yet available in the literature. Objective. The present study investigates the role of SPA on loneliness and the moderating effects of narcissistic personality and family belonging on loneliness. Participants and Setting. Data required for research were obtained via an online survey from undergraduate students (n = 500) studying at a public university. Methods. In the study, the relationship between the variables was determined by path analysis. Results. The results of the path analysis show that there is a significant positive relationship between SPA and loneliness. According to the model, no significant relationship was found between narcissistic personality and family-belonging level. There is a negative and significant mediation effect between SPA and narcissistic personality traits. There is a positive and significant mediation effect between SPA and family belonging. The results of the research are discussed with regard to university students and future directions. Conclusions. According to these research results, SPA predicts loneliness. As the level of family belonging decreases, SPA increases. The relationship between university students and their families and environments is among the variables that should be considered when evaluating SPA.Smartphone usage rates have displayed a rapid increase around the world in the last decade. In the We Are Social Digital Report of 2020, it was revealed that the global number of mobile phone users has reached 5.19 billion; 70 percent of those are smartphone users and the daily average mobile phone usage time is 3 hours 40 minutes (We Are Social, 2020). Over time, this intense usage of smartphones may cause individuals to become overly connected to their phones (