The microRNAs (miRNAs/miRs) are a class of short non-coding RNAs regulating protein translation via mRNAs silencing. Studies have shown that microRNAs play critical roles in allergic diseases, tumors, and infections. The allergic airway diseases are characterized by inflammation and hyperresponsiveness of the respiratory tract. Several miRNAs are found to be involved in a series of pathophysiologic processes in allergic airway diseases including inflammatory cells infiltration, cytokines' expressions, airway hyperresponsiveness, and proliferation and change in phenotype of smooth muscle cells. Therefore, miRNAs may be new therapeutic targets for these allgeric diseases. This article reviews the roles of miRNAs in asthma and allergic rhinitis and their molecular biological mechanisms.