ObjectiveTo investigate the association between carbohydrate antigen 125 (CA125) level and adenomyosis treatment failure (TF) after uterine artery embolization (UAE).MethodsWe evaluated 224 patients with symptomatic adenomyosis who underwent UAE between January 2016 and December 2020. Improvements in dysmenorrhea and menorrhagia were assessed on the basis of symptom relief criteria. The factors associated with TF were investigated using a multivariate logistic regression model. Patients were analyzed for preoperative CA125 levels, postoperative CA125 levels, and the normalization of postoperative CA125 levels. Long‐term symptom relief and quality of life after UAE were compared between the groups.ResultsDuring the 24‐month follow‐up, 50 patients (22.3%) experienced TF. Compared to patients in the non‐TF group, those in the TF group had significantly higher preoperative and postoperative CA125 levels (p < 0.05). Multivariate analysis revealed that failure to normalize postoperative CA125 levels was independently associated with an increased risk of TF (34.7% vs. 8.5%, p < 0.001; hazard ratio 3.953, 95% confidence interval 1.567–9.973, p = 0.004). After a 3‐month follow‐up period, patients who normalized their CA125 levels were more likely to achieve complete necrosis on magnetic resonance imaging than those who did not (82.1% vs. 56.8%, p < 0.001). Normalization of postoperative CA125 levels was significantly associated with fewer symptoms and better quality of life 12 months after UAE (p < 0.05).ConclusionsFollowing UAE, normalization of postoperative CA125 levels, rather than absolute values, was the strongest predictive marker of TF.