Background Many patients undergo dose reduction or early termination of chemotherapy to reduce chemoradiotherapy-related toxicity, which may increase their risk of survival. However, this strategy may result in underdosing patients with locally advanced esophageal squamous cell carcinoma (LA-ESCC). This study aimed to analyze the relationship between the relative dose intensity (RDI) and survival outcomes in patients with LA-ESCC. Methods This retrospective study assessed patients with LA-ESCC (cT2N + M0, cT3-4NanyM0) receiving neoadjuvant chemoradiotherapy (NCRT) with curative-intent esophagectomy. The patients received 2 courses of paclitaxel plus carboplatin (TC) combination radiotherapy prior to undergoing surgery. During NCRT, RDI was computed, defined as the received dose as a percentage of the standard dose, and the incidence of dose delays was estimated (>= 7 days in any course cycle). The best RDI cutoff value (0.7) was obtained using ROC curve. The Kaplan-Meier survival curves were compared using the log-rank test, the treatment effect was measured using hazard ratios (HR) and 95% confidence intervals (CI). Results We included 132 patients in this study, divided into RDI < 0.7 and RDI >= 0.7 groups using cut-off value of 0.7. RDI grade was an independent prognostic factor for OS. Baseline demographic and clinical characteristics were well balanced between the groups. There was no evidence that patients with RDI < 0.7 experienced less toxicity or those with RDI >= 0.7 resulted in more toxicity. However, patients with RDI < 0.7 who were given reduced doses had a worse overall survival [HR 0.49, 95% CI 0.27-0.88, P = 0.015]. The risk of a lower RDI increased with a longer dose delay time (P < 0.001). Conclusion The RDI below 0.7 for avoiding chemoradiotherapy toxicity administration led to a reduction in the dose intensity of treatment and decreased overall survival.