Social networking sites (SNSs) enrol new subscribers each day. However, problematic SNS use has undesirable effects on psychological functioning. Therefore, it is important to identify the factors that contribute to the development of problematic SNS use. Very few studies have focused on revealing the underlying mechanisms of problematic SNS use. Although many past studies have examined the relationship between metacognitive beliefs and Internet addiction, the association between metacognitive beliefs and problematic SNS use has not been adequately explored. In this study, we aimed to explore the association between metacognitive beliefs and problematic SNS use among young adults. A total of 308 individuals participated in this study. A socio-demographic data form, the Metacognitions Questionnaire-30 (MCQ-30), and Social Media Addiction Scale (SMAS) were administered. Group comparisons were performed using multivariate analysis of covariance. Pearson's correlational and multiple linear regression analyses were conducted to examine the associations between metacognitive beliefs and problematic SNS use. The SNS addicts scored higher in all of the SMAS assessments. When compared to non-addicts, SNS addicts obtained higher scores on all the subtests of the SMAS and MCQ-30 except cognitive self-consciousness. The negative beliefs about the uncontrollability and danger of worry, cognitive confidence, and need for control thoughts were associated with SMAS mood modification, relapse and conflict subdimensions. Our findings revealed that dysfunctional metacognitive beliefs are related to problematic SNS use among young adults. These findings indicate that mental health workers should consider the modification of metacognitive beliefs in the treatment of problematic SNS use. © 2020 Scandinavian Psychological Associations and John Wiley & Sons Ltd.