Objective: To analyze the association between posttreatment squamous cell carcinoma antigen (SCC Ag) and treatment failure in patients with cervical SCC treated with concurrent chemoradiotherapy (CCRT). Methods: We reviewed patients with cervical SCC who were treated with definitive radiotherapy or CCRT between June 2012 and May 2015 at our institute. A receiver operating characteristic (ROC) curve was used to analyze the cutoff value of posttreatment SCC Ag in predicting treatment failure. Log-rank tests and Cox proportional hazards models were used to identify whether posttreatment SCC Ag was significant in predicting disease-free survival (DFS). Results: A total of 559 patients were included in this study. With the ROC curve, the optimal cutoff posttreatment SCC Ag level was 1.8 ng/mL (sensitivity 27.1%, specificity 96.6%). A posttreatment SCC Ag level ≥ 1.8 ng/mL was observed in 47 patients. The multivariate analysis showed that posttreatment SCC Ag (hazard ratio 5.10; 95% confidence interval, 3.31–7.88; p < 0.001) was an independent prognostic factor of DFS. The 3-year overall survival (OS), DFS, local control, and distant control rates of patients with posttreatment SCC Ag < 1.8 ng/mL and ≥1.8 ng/mL were 90.7% and 46.4% (p < 0.001), 84.8% and 31.9% (p < 0.001), 81.4% and 69.5% (p < 0.001), and 90.4% and 54.1% (p < 0.001), respectively. Conclusion: Patients with posttreatment SCC Ag ≥ 1.8 ng/mL suffer due to a high rate of treatment failure and poor survival. © 2019 Elsevier Inc.