Background: Metacognitive therapy (MCT) is an evolving therapeutic approach that has shown promise in the treatment of generalized anxiety disorder (GAD). Accordingly, this study aimed to assess the impact of MCT on rumination, self-concept, and perceived social support (PSS) in women diagnosed with GAD. Methods: The current quasi-experimental study was conducted using a pre-test-post-test design with a control group. The statistical population consisted of women diagnosed with GAD in Tehran in 2022. The research sample comprised 36 women with GAD, selected through purposive sampling and allocated into an experimental group (n=18) and a control group (n=18). The experimental group underwent ten 90-minute sessions of MCT, while the control group received no intervention. Data were collected through questionnaires to assess GAD symptoms, rumination, self-concept, and PSS. The collected data were analyzed using multivariate analysis of covariance (MANCOVA) via SPSS version 24. Results: The findings indicated that MCT led to a significant decrease in rumination from 53.61±3.25 to 48.94±3.45 (P<0.001) and an increase in self-concept from 70.55±2.87 to 74.16±2.74 (P<0.001) among women diagnosed with GAD. Additionally, the dimensions of PSS were significantly enhanced: support from significant others increased from 15.72±1.34 to 18.50±1.20 (P<0.001), family support increased from 17.78±1.22 to 20.50±1.91 (P<0.001), and support from friends increased from 16.22±1.74 to 19.01±1.30 (P<0.001). Conclusion: The findings from this study underscore the potential of MCT as a tailored intervention for enhancing well-being and reducing anxiety in individuals diagnosed with GAD, highlighting its relevance for clinical practice and future research endeavors.