Bronchial asthma is a common chronic inflammatory airway disease. Small airway dysfunction (SAD) can be present in asthmatics with different phenotypes, clinical stages and varied severity, and has implication for drug efficacy and patient prognosis. Currently, there is no consensus on the criteria for SAD, and its inflammatory mechanism remains unclear. In this paper, we reviewed the research advances in the evaluation, prevalence, pathogenesis, clinical features and treatment of SAD in asthmatics to improve awareness of the disease.