Oxidative stress has been implicated in the pathogenesis and progression of chronic obstructive pulmonary disease. Both reactive oxidant species from inhaled cigarette smoke and those endogenously formed by inflammatory cells constitute an increased intrapulmonary oxidant burden. Structural changes to essential components of the lung are caused by oxidative stress, contributing to irreversible damage of both parenchyma and airway walls. In addition, oxidative stress results in alterations in the local immune response, increasing the risk of infections and exacerbations, which, in turn, may accelerate lung function decline. The antioxidant N‐acetylcysteine, a glutathione precursor, has been applied in these patients in order to reduce symptoms, exacerbations and the accelerated lung function decline. This article reviews the presently available experimental and clinical data on the antioxidative effects of N‐acetylcysteine in chronic obstructive pulmonary disease.