Fear of Missing Out (FoMO) refers to an individual’s concern about missing out on desirable experiences and opportunities that they perceive others to be experiencing. In recent years, particularly with the widespread use of social media, FoMO has become an increasingly important topic in the field of mental health. University students, due to being in a developmental period characterized by academic, social, and identity-related changes, may be more vulnerable to social experiences and comparisons with others. The present study aims to investigate the role of rumination in the relationship between Fear of Missing Out and symptoms of depression and anxiety among Iranian university students, with particular attention to the moderating role of emotion regulation. This study will employ a descriptive-correlational design. The study population will consist of university students in Iran, and the sample will be selected using an appropriate sampling method. Data will be collected using the Fear of Missing Out Scale, the Ruminative Responses Scale, the Emotion Regulation Questionnaire, the Beck Depression Inventory-II, and the Depression Anxiety Stress Scales. The data will be analyzed using appropriate statistical methods to examine the direct and indirect relationships among the variables, as well as the mediating role of rumination and the moderating role of emotion regulation. The findings are expected to contribute to a more precise understanding of the cognitive and emotional mechanisms associated with university students’ mental health and to the identification of vulnerability and protective factors related to symptoms of depression and anxiety.