Background: While brachytherapy stands as a crucial component of the treatment for locally advanced cervical cancer, the issue of geographic disparities in brachytherapy accessibility has become a noteworthy public health concern in South Korea. Moreover, the specific factors contributing to these disparities have not been clearly elucidated. In light of this, we conducted a nationwide ecologic study to comprehensively investigate the socioeconomic factors associated with brachytherapy accessibility. Methods: A total of 2,998 patients newly diagnosed with cervical cancer in 2020 were identified through the Korea Central Cancer Registry (KCCR). Across 17 administrative districts in South Korea, 32 brachytherapy facilities were available. To capture unique socioeconomic factors for each region, including the number of Korean Medicaid (K-Medicaid), Medicare (K-Medicare) beneficiaries, marriage immigrants, registered foreigners, and total residents, data were obtained from the Korean Statistical Information Service (KOSIS). Notably, K-Medicaid and K-Medicare represent governmental medical insurance assistance for patients in poverty and those aged over 65, respectively. The brachytherapy accessibility rate (BAR) was defined as the number of brachytherapy procedures divided by new cervical cancer cases. Additionally, each district's socioeconomic factor was normalized by the number of residents. Univariate and multivariate logistic regression analyses were conducted to explore the relationships between BAR and socioeconomic factors. Results: The capital city and its adjoining metropolitan area accounted for 46.9% of the total brachytherapy facilities, with Seoul having 25% (8 out of 32) and Gyeonggi having 21.9% (7 out of 32). Conversely, three non-metropolitan regions had no brachytherapy facilities. In the multivariate logistic regression analysis, the brachytherapy accessibility rate (BAR) demonstrated an inverse association with both the number of K-Medicare beneficiaries and the total immigrant population (Odds ratios of 0.66 and -2.85, respectively). Conclusions: To the best of our knowledge, this is the inaugural study highlighting the robust associations between older age and foreign residency status with reduced accessibility to brachytherapy. The observed inaccessibility to brachytherapy has the potential to impede the delivery of standard care, consequently leading to a poorer prognosis for vulnerable populations. Future research endeavors and targeted social interventions will be imperative to rectify geographic disparities in brachytherapy accessibility and ensure equitable healthcare outcomes.