Copyright © 2015 by the American Thoracic Society Asthma is a disease of acute and chronic inflammation in which cytokines play a critical role in orchestrating the allergic inflammatory response. IL-13 and transforming growth factor (TGF)-β promote fibrotic airway remodeling, a major contributor to disease severity. Improved understanding is needed, because current therapies are inadequate for suppressing development of airway fibrosis. IL-13 is known to stimulate respiratory epithelial cells to produce (TGF)-β, but the mechanism through which this occurs is unknown. Here, we tested the hypothesis that reactive oxygen species (ROS) are a critical signaling intermediary between IL-13 or allergen stimulation and (TGF)-β-dependent airway remodeling. We used cultured human bronchial epithelial cells and an in vivo mouse model of allergic asthma to map a pathway where allergens enhanced mitochondrial ROS, which is an essential upstream signal for (TGF)-β activation and enhanced collagen production and deposition in airway fibroblasts. We show that mitochondria in airway epithelium are an essential source of ROS that activate (TGF)-β expression and activity. (TGF)-β from airway epithelium stimulates collagen expression in fibroblasts, contributing to an early fibrotic response to allergen exposure in cultured human airway cells and in ovalbumin-challenged mice. Treatment with the mitochondrial-targeted antioxidant, (2-(2,2,6,6-Tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride (mitoTEMPO), significantly attenuated mitochondrial ROS, (TGF)-β, and collagen deposition in OVA-challenged mice and in cultured human epithelial cells. Our findings suggest that mitochondria are a critical source of ROS for promoting (TGF)-β activity that contributes to airway remodeling in allergic asthma. Mitochondrial-targeted antioxidants may be a novel approach for future asthma therapies.