This study aimed to characterize postoperative blood glucose fluctuation in patients who underwent esophagectomy for esophageal cancer, and to define its impact on complications and prognosis. The subjects of this retrospective study were 284 patients who underwent esophagectomy at Osaka University Hospital between 2015 and 2017. Data analyzed included clinicopathological background, the immediate postoperative blood glucose level (IPBG), postoperative blood glucose variability (PBGV), insulin dosage, postoperative complications, and prognosis. The median IPBG and PBGV were 170 (64-260) mg/dl and 64.5 (11-217) mg/dl, respectively. Postoperative pneumonia was more common in patients with PBGV > 100mg/dl (P = 0.015). Patients with IPBG < 170mg/dl had significantly worse 5-year overall survival (OS) and 5-year recurrence-free survival (RFS) than those with IPBG > 170mg/dl (54.5% vs. 80.4%, respectively, [P < 0.001] and 44.3% vs. 69.3%, respectively, [P = 0.001]). The 5-year OS rates were 43.5%, 68.3%, 80.6%, and 79.0% for patients with IPBG < 154, 154-170, 170-190, and ≥ 190mg/dl, respectively. The corresponding 5-year RFS rates were 38.1%, 52.4%, 77.0%, and 61.3%, respectively. Multivariate analysis revealed that IPBG < 154mg/dl and pathological stage were independent poor prognostic factors for OS. PBGV was associated with postoperative pneumonia, and low IPBG was an independent poor prognostic factor for patients with esophageal cancer.