Social anxiety is one of the most prevalent psychological problems during young adulthood, particularly among university students, and may adversely affect academic performance, interpersonal relationships, and mental health. The present study aimed to investigate the mediating role of alexithymia in the relationship between metacognitive beliefs and social anxiety among female university students. This descriptive correlational study was conducted on 384 female students enrolled at the Tehran West Branch of Islamic Azad University during the spring semester of 2025, who were selected using convenience sampling. Data were collected using the Short Form of the Metacognitions Questionnaire (MCQ-30), the Toronto Alexithymia Scale (TAS-20), and the Social Phobia Inventory (SPIN). Data were analyzed using Pearson’s correlation coefficient and structural equation modeling (SEM). The findings indicated that metacognitive beliefs were positively and significantly associated with both alexithymia and social anxiety. Furthermore, alexithymia was positively associated with social anxiety. The indirect effect of metacognitive beliefs on social anxiety through alexithymia was also significant, indicating the partial mediating role of alexithymia in this relationship. Overall, the findings suggest that maladaptive metacognitive beliefs contribute to increased social anxiety both directly and indirectly through greater difficulties in identifying and describing emotions. These results highlight the importance of addressing metacognitive beliefs and emotional processing deficits in the development of preventive and therapeutic interventions aimed at reducing social anxiety among female university students.