Background: In Mongolia, cervical cancer accounted for 11.9% of all cancers diagnosed in women and 7.3% of cancer-related deaths in 2017, ranking as the third most common cancer among women. The American Society for Radiation Oncology (ASTRO) guidelines recommend concurrent chemo-radiotherapy (CCRT) as a standard and effective treatment for patients with FIGO stage IB3–IVA cervical cancer. Accurate assessment of tumor response following CCRT is essential for evaluating treatment efficacy, identifying residual disease, and estimating the risk of recurrence. Magnetic resonance imaging (MRI) is widely used to assess tumor size, local extent, parametric involvement, and post-treatment morphological changes. In contrast, 18F-FDG PET/CT provides both anatomical and functional information and enables quantitative assessment of tumor metabolic activity using the standardized uptake value (SUV). Aim: To estimate the relationship between treatment response to concurrent chemo-radiotherapy and radiological parameters obtained from MRI and 18F-FDG PET/CT in patients with cervical cancer. Materials and Methods: This retrospective study included 35 patients with histo-pathologically confirmed cervical carcinoma who received concurrent chemo-radiotherapy at the Department of Radiation Oncology, National Cancer Center, between 2024 and 2025. Pelvic MRI examinations were performed using a 1.5-T Siemens MRI system to evaluate tumor dimensions and local tumor characteristics before and after treatment. 18F-FDG PET/CT was performed to assess the metabolic activity of the primary tumor, and the maximum SUV was measured. Tumor response following CCRT was evaluated according to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. The relationships between tumor response, changes in tumor size, and pre-treatment SUV were statistically analyzed. Result: A total of 35 patients aged 32–73 years were included in the study, with a mean age of 51.2±12.6 years. The mean baseline longitudinal tumor diameter measured by MRI was 54.3±15.8 mm. Twenty-eight patients (80.0%) had tumors larger than 4 cm, whereas 7 (20.0%) had tumors smaller than 4 cm. According to the FIGO staging system, 22 patients (62.9%) had stage IIIC1 disease, 7 (20.0%) had stage IIIC2, 3 (8.6%) had stage IIIB, 2 (5.7%) had stage IIB, and 1 (2.9%) had stage IVA disease. Histopathologically, 31 patients (88.6%) had squamous cell carcinoma, 3 (8.6%) had adenocarcinoma, and 1 (2.9%) had clear cell carcinoma. Of the 35 patients, 23 (65.7%) had reached the scheduled post-treatment follow-up time and were evaluable for treatment response according to RECIST 1.1, whereas 12 patients (34.3%) had not yet reached the scheduled time for post-treatment assessment. Among the 23 evaluable patients, 15 (65.2%) achieved a complete response (CR), while 8 (34.8%) achieved a partial response (PR). Following CCRT, the longest tumor diameter measured by MRI decreased by a mean of 94.8% in the CR group and 65.3% in the PR group. The reduction in tumor diameter was significantly greater in the CR group than in the PR group (p=0.0016). The mean baseline primary tumor SUVmax on 18F-FDG PET/CT was 16.0±9.8 in the CR group and 24.3±14.5 in the PR group. Although the baseline SUVmax tended to be lower in the CR group, the difference did not reach statistical significance (Mann–Whitney U test, p=0.059). A higher baseline SUVmax tended to be associated with a smaller reduction in tumor diameter following CCRT. Conclusion CCRT resulted in a significant reduction in primary tumor size in patients with cervical cancer. The reduction in tumor size was significantly greater among patients who achieved a complete response than among those who achieved a partial response. Although pre-treatment 18F-FDG PET/CT findings suggest that MRI-based tumor size assessment combined with metabolic information from 18F-FDG PET/CT may provide complementary information for evaluating treatment response following CCRT.