An esophagobronchial fistula, an abnormal passageway formed between the esophagus and bronchus, can cause severe respiratory symptoms. This fistula is a complication that can occur during chemoradiotherapy for esophageal and lung cancers; however, to our knowledge, no esophagobronchial fistulas during preoperative chemotherapy for lung cancer have been reported. The patient was a 55-year-old man whose chest computed tomography (CT) revealed a mass on the dorsal bronchus and right side of the esophagus. A transesophageal needle biopsy confirmed the diagnosis of lung adenocarcinoma, and preoperative chemotherapy, which included pembrolizumab, was administered. One week after the first course of chemotherapy, the patient developed a severe cough after drinking water. Chest CT revealed an esophagobronchial fistula, which prompted the discontinuation of the preoperative chemotherapy. Subsequent conservative treatment resulted in no improvement, and the patient was referred to our department. One month thereafter, a two-stage reconstruction of the esophagus was performed via the posterior sternal route. The resected specimen showed no residual tumor in the lungs, and the treatment was determined to result in a complete pathological response. The patient is currently undergoing maintenance therapy with pembrolizumab as a single agent. This is a rare case of esophagobronchial fistula identified during preoperative chemotherapy that included pembrolizumab for lung cancer. In addition to suturing the fistula, filling it with a distal hyoid valve was effective in treating the esophagobronchial fistula.