Reactive oxygens are now considered to be important substances in promoting inflammatory process. Recently, airway inflammation has attracted attention closely linked to bronchial asthma. The present study was undertaken to examine whether hydrogen peroxide, one of the reactive oxygens, could produce airway inflammation. Airway inflammation was assessed by airway vascular permeability in terms of pontamine sky blue (PSB) exudation. Airway resistance was measured with a modified Konzett‐Rössler method and was expressed as a change in ventilation overflow. Inhalation of hydrogen peroxide (0.01–1.0 M) markedly caused a PSB exudation in a concentration‐dependent manner in all of the trachea, main bronchus, and lungs. The hydrogen peroxide‐induced PSB exudation effect was attenuated by pretreatment with catalase, although heat‐inactivated catalase had no inhibitory effect. Deferox‐amine, which inhibits conversion of hydrogen peroxide into hydroxyl radical, decreased the PSB exudation induced by hydrogen peroxide. On the other hand, inhalation of hydrogen peroxide (1.0 M) caused a significant and biphasic increase in ventilation overflow. This airway constriction was suppressed by pretreatment with inhaled catalase, but not by inhaled deferoxamine. These results indicate that hydrogen peroxide causes an intense airway inflammation; this inflammatory effect may be mediated not only by hydrogen peroxide itself but also by hydroxyl radical. Hydrogen peroxide and hydroxyl radical may thus play an important role in bronchial asthma and bronchitis through inducing airway inflammation.