There has been growing concern regarding the effects of ambient air pollution on asthma. Particulate matter (PM) is one of the major air pollutants affecting both general population and the patients with asthma. This paper reviews the recent evidence of the adverse effects of PM on the inception and morbidity of asthma. Epidemiological studies confirmed that short-term exposure to PM aggravated respiratory symptoms and lung function in asthma patients. Furthermore, PM induces acute exacerbations of asthma with increased risk of hospitalization and death. Long-term exposure to PM is responsible for new onset of asthma and lung function decline in both children and adults. Various mechanisms are involved in the effects of PM on airway including oxidative stress, augmentation of inflammation, promotion of allergen sensitization, induction of airway hyperresponsiveness, aggravation of rhinitis and DNA methylation. Special attention and care is needed for the patients with asthma to prevent the detrimental effects of PM. (Allergy Asthma Respir Dis 2015;3:313-319)