In the current study, it was aimed to examine the relationships between individuals' fear of COVID-19, fear of missing out (FoMO), and ruminative thought style levels. The participants consisted of 408 individuals aged between 17-68, of which 110 were male and 298 were female. In this study, The Fear of COVID-19 Scale, Fear of Missing Out Scale, and Ruminative Thought Style Questionnaire were used in order to collect data. Relational survey method was used in the research. In the mediation analysis, it was observed that the ruminative thought style has a mediator role in the relationship between FoMO and fear of COVID-19. According to the findings, women have a higher fear of COVID-19 and ruminative thought style levels than men, besides that married individuals' fear of COVID-19 level is higher than single individuals, but FoMO and ruminative thought levels are lower.