Purpose: Accumulating evidence suggests that microbiota dysbiosis induced by antibiotic administration plays a crucial role in regulating the efficacy and toxicity of cancer therapy. We explored the influence of antibiotic administration on the efficacy of chemotherapy in patients with esophageal cancer (EC). Patients and Methods: EC patients were stratified into two groups: antibiotic-treated group and control group. The antibiotic-treated group included patients who received antibiotics within 60 days before or after chemotherapy initiation, and the control group included patients who did not receive antibiotics within 60 days before or after chemotherapy initiation. Progression-free survival (PFS) and overall survival (OS) curves were constructed using the Kaplan-Meier method. The Cox proportional hazards model was used for univariate and multivariate analyses. Results: The rate of primary progressive disease in the antibiotic-treated group was significantly higher than that in the control group (36.58% vs 10.45%, p = 0.002) as calculated using the chisquare test. Further, antibiotic administration was associated with shorter PFS (6.7 vs 14.6 months, hazard ratio (HR): 2.545, 95% confidence interval (CI): 1.554-4.168, p < 0.001) and reduced OS (15.0 vs 21.0 months, HR: 2.007, 95% CI: 1.213-3.319, p = 0.007) in univariate analysis. Subsequent multivariate analysis indicated that antibiotic administration was a significant independent prognostic factor for PFS (HR: 2.350, 95% CI: 1.423-3.882, p = 0.001) and OS (HR: 1.900, 95% CI: 1.140-3.167, p = 0.014). Conclusion: Antibiotic administration was associated with reduced chemotherapy efficacy and poor prognosis in patients with EC.