The development of social media websites is constantly attracting the online users especially the young adults. Features of social media websites offer varied information that compel individuals to do social comparison with others. The goal of this study is to examine the effect of fear of missing out on the psychological well-being of young adults. Previous studies have investigated the correlations among various variables of social media websites however there exist a gap on causal relationship studies in previous literature. To bridge this gap, researcher has used hypothesized serial mediation model and for this study researcher has incorporated Fear of missing out (FoMO) as independent and psychological wellbeing (anxiety and depression) as dependent variable while considering the mediating role of compulsive use and social comparison into the model. Data was collected from a sample of 400 university students. Results indicate that there exists a direct positive relationship between each component of model. Moreover, indirect links show that there exists a mediation as well. Compulsive use and social comparison jointly mediate the relation between FoMO and psychological well-being. Increase in compulsive use will allow individuals to do more comparisons which in turn cause more anxiety and depression among young adults.