Detection of the fraction of exhaled nitric oxide (FeNO) is a safe, simple and easy method to assess airway inflammation noninvasively. Thus, FeNO detection has been paid more attention to diagnosis and guide treatment of pulmonary diseases. The common feature of pneumonia, asthma, chronic obstructive pulmonary disease and chronic cough is the existence of varying degrees of airway inflammation. In this review, FeNO production and its potential pathologic and physiologic role in various pulmonary diseases were discussed.