OBJECTIVE: Gastric-type mucinous carcinoma (GAS) is a novel variant of uterine cervix mucinous carcinoma. GAS is a distinct entity that can be distinguished from typical endocervical adenocarcinoma (UEA). In Japan, postoperative adjuvant therapy for cervical cancer includes not only radiation therapy (RT) or concurrent chemoradiotherapy (CCRT) but also chemotherapy in many cases. However, no previous studies have analyzed adjuvant therapy for GAS. In the present study, we investigated the efficacy of adjuvant therapy for GAS. METHODS: This was a preplanned secondary analysis of a dataset from previous nationwide, retrospective, observational study. The study population comprised women with stage I-II GAS who underwent surgery. Progression-free survival (PFS) and overall survival (OS) were compared among patients who did and did not receive adjuvant therapy using the Kaplan-Meier method. RESULTS: Data were analyzed for a total of 102 enrolled patients, who were classified as low- (17 patients), intermediate- (37 patients), or high risk (48 patients) based on the risk of postoperative cervical cancer recurrence. In the intermediate-risk group, median survival could not be assessed due to a lack of sufficient events, but the no-adjuvant and RT groups tended to exhibit better prognoses. In contrast, within the high-risk group, patients in the RT subgroup exhibited a trend towards better PFS and OS than those in the CCRT and chemotherapy groups. CONCLUSIONS: The prognosis of GAS was confirmed to be poor, even in cases of early-stage cancer and following surgical resection. Chemotherapy strategies, including CCRT as postoperative adjuvant therapy, tend to have a poor prognosis.