With the increase in smartphone use, smartphone addiction has gained immense popularity and there has been a lot of research into smartphone addiction. Nonetheless, research examining the complex relationships between cyberloafing and smartphone addiction is still insufficient. Thus, the present study aims to establish the mediating role of fear of missing out, which is a cognitive and emotional process, in the effect of university students' level of cyberloafing upon their smartphone addiction level. The study group of the research is represented by 338 students receiving formation training in the faculty of education, at a state university. For the purpose of data collection, the Smartphone Addiction Scale - Short version, the Cyberloafing Scale, and the Fear of Missing Out Scale were used. The model was tested using structural equation modeling and bootstrapping. Structural equation modeling results provide evidence of indirect effects of cyberloafing on smartphone addiction partial mediated by fear of missing out. According to the Bootstrapping method, fear of missing out has an indirectly significant role in the relationship between cyberloafing and smartphone addiction. The findings emphasized the role of fear of missing out in explaining the relationship between cyberloafing and smartphone addiction. The study concludes by discussing relevant conclusions in the literature, and putting forth several recommendations based on these conclusions.