Background: Mucous hypersecretion increases asthma morbidity and mortality. Tumor necrosis factor α (TNF-α) levels are elevated in bronchoalveolar fluid, sputum, and monocyte membranes in some patients with asthma. Anti-TNF-α decreased asthma exacerbations and improved forced expiratory volume in 1 second in these patients. Whether anti-TNF-α reduces mucous cell metaplasia or hyperplasia has not been evaluated. Objective: To investigate the role of anti-TNF-α in mucous hypersecretion. Methods: BALB/c mice sensitized intraperitoneally and challenged intratracheally with ovalbumin were treated with 250 μg of anti-TNF-α before ovalbumin sensitization and challenge or before only ovalbumin challenge. Control groups were sham treated. The tumor necrosis factor receptor (TNFR) mice (TNFR-/- and TNFR+/+) were identically sensitized and challenged. Seventy-two hours after the final challenge, the airway pressure time index (APTI), which measures airway hyperresponsiveness, was recorded. Mucous cell metaplasia was accessed by quantitative polymerase chain reaction for MUC-5AC (the epithelial cell mucous-inducing gene) and the percentage of periodic acid-Schiff (PAS) staining of bronchial epithelial cells. A human airway cell line (constitutively expressing MUC-5AC) was pretreated with a NF-κB inhibitor before TNF-α culture. Results: The mean (SE) fold change of MUC-5AC expression (compared with naive controls), the percentage of PAS-positive bronchiole epithelial cells, and the APTI decreased in BALB/c mice treated with anti-TNF-α before sensitization and challenge (4.9 [1.14], P = .007; 28.9% [6.8%], P < .001; and 545.8 [104.5] cm H2O/s, P < .001, respectively) and before challenge alone (9.3 [1.8], P = .03; 43.6% [10.7%], P = .009; and 896.8 [81.23] cm H2O/s, P = .06, respectively) compared with sham-treated mice (20.9 [3.9], 82.4% [1.8%], and 1,055 [30.6] cm H 2O/s, respectively). MUC-5AC expression decreased in ovalbumin sensitized or challenged TNFR-/- (2.41 [0.4]) compared with ovalbumin sensitized or challenged TNFR+/+ mice (18.4 [2.5], P < .001). TNF-α-induced MUC-5AC expression in human airway culture significantly decreased with pretreatment of a NF-κB inhibitor. Conclusions: Anti-TNF-α treatment reduces airway mucous cell metaplasia in a mouse model of asthma, which may in part underlie its beneficial effect as asthma therapy.