Expiratory flow is an important factor in the achievement of airway clearance that is required to prevent postoperative pneumonia (POP). Although peak expiratory flow (PEF) has been shown to predict the occurrence of POP in lung cancer patients after lobectomy, its predictive power in relation to esophagectomy for esophageal cancer remains unknown. This study assesses PEF as a predictor of POP in patients with esophageal cancer undergoing radical esophagectomy. We conducted a single-center, retrospective cohort study of patients who underwent radical esophagectomy with gastric tube reconstruction at our institution between January 2007 and December 2022. Preoperative pulmonary functions, including PEF, were assessed before surgery. Additionally, POP was diagnosed as a Clavien-Dindo classification of Grade II or higher. Survival and pneumonia incidence were compared using the Kaplan-Meier method. Logistic regression analysis was used to examine the relationship between these variables and POP. The study included 513 patients, of which 441 were men. POP occurred in 86 patients (16.7%). When all patients were stratified by %PEF into two groups, the group with %PEF lower that 80% had significantly poorer prognosis and higher incidence of pneumonia. Multivariable logistic regression analysis indicated that %PEF (OR: 0.986, 95%CI: 0.974-0.999, P = 0.030), along with age, BMI, preoperative treatment, and recurrent laryngeal nerve palsy were independent protective factors against POP. These results reveal that %PEF predicts the development of POP following esophagectomy for esophageal cancer.