Non-cystic fibrosis bronchiectasis is characterized by the irreversible dilatation of the medium-sized bronchi as a result of airway injury from recurrent or chronic inflammation and lower respiratory tract infections. Bronchiectasis airways are commonly colonized with bacterial species. Infections of the airways play important role in bronchiectasis exacerbations. The non-specific prevention of recurrent airway infections by immunostimulating agents has gained growing interest. OM-85, consisting of extracts of eight kinds of bacteria important in respiratory infections, could support the respiratory tract resistance to the pathogens. OM-85 has been shown to be a benefit by decreasing the risk of acute exacerbation of chronic obstructive pulmonary disease (COPD) in several perspective clinical trials. Exacerbation of bronchiectasis substantially contributes to a more rapid decline in lung function, reduced quality of life, and healthcare costs. In this context, we plan to conduct a clinical trial to investigate the PReventive effect of OM-85 on Bronchiectasis Exacerbation in Chinese patients (iPROBE).