Aim: Definitive chemoradiotherapy (dCRT) is the standard treatment for locally advanced unresectable esophageal squamous cell carcinoma (LU-ESCC). This study aimed to describe the results of dCRT for T4 ESCC and evaluate the pretherapeutic predictive factors of the outcomes. Methods: A total of 133 patients with T4 ESCC who received dCRT were grouped into those who achieved a complete response (CR) or those who had residual disease (RD). The clinicopathologic variables were compared between the groups and the overall survival (OS) was evaluated. The predictive factor of RD was assessed and the prognostic factor for OS was identified. Results: Among the 133 patients, 31 (23%) achieved CR. The CR group had a significantly better OS than the RD group (89.9 months vs. 10.7 months; hazard ratio = 0.096; 95% confidence interval: 0.05-0.19; P < 0.001). Multivariate analysis showed that a supracarinal tumor (OR = 3.21; P = 0.016), higher pretherapeutic serum SCC-Ag level (> 1.6 ng/mL) (OR = 2.86; P = 0.018), and metastatic node invasion (OR = 3.19; P = 0.048) were independent predictors of RD. The increased level of pretherapeutic serum squamous cell carcinoma antigen (> 1.6 ng/mL) (OR = 1.61; P = 0.022) was an independent predictor of poor survival. Conclusions: Among the patients who underwent dCRT for LU-ESCC, 23% achieved CR, and the long-term outcome of these patients was favorable. Increased levels of pretherapeutic serum squamous cell carcinoma antigen were also found to be predictive of treatment failure.