Given the vulnerability to and prevalence of emotional problems and Internet gaming disorder (IGD) in adolescents, this study aimed to test the effects of fear of missing out (FoMO) on IGD and the mediating roles of metacognitive beliefs and anxiety symptoms based on the self-regulatory executive function (S-REF) model. At a Chinese high school, 283 participants (M = 16.89 years old; girls = 42.0%) with past-year gaming experience voluntarily completed an anonymous paper-and-pencil questionnaire. FoMO showed significant, positive associations with IGD, anxiety symptoms, and metacognitive beliefs. Results of path analysis showed a significant direct effect of FoMO on IGD, whereas anxiety symptoms mediated the relationship between FoMO and IGD. The indirect effects of FoMO on IGD via serial mediations of three negative metacognitive beliefs (i.e., negative beliefs about worry, low cognitive confidence, and beliefs regarding need for control) and anxiety symptoms were also statistically significant. These findings demonstrated that maladaptive metacognitive beliefs and anxiety are risk-enhancing mediators in the relationship between FoMO and IGD. Therefore, metacognitive therapy, particularly for regulating those three specific significant metacognitive beliefs, is recommended for treating IGD and anxiety, especially for those with higher levels of FoMO.