Airway mucus obstruction is a hallmark of chronic lung diseases such as cystic fibrosis, asthma and COPD, and the development of more effective mucus mobilizing therapies remains an important unmet need for patients with these muco-obstructive lung diseases. However, methods for sensitive visualization and quantitative assessment of immediate effects of therapeutic interventions on mucus clearance are lacking. In this study, we determined if newly developed high-speed microscopic optical coherence tomography (mOCT) is sensitive to detect and compare effects of inhaled isotonic saline, hypertonic saline and bicarbonate on mucus mobilization and clearance in -transgenic mice with muco-obstructive lung disease. mOCT imaging showed that inhaled isotonic saline-induced rapid mobilization of mucus that was mainly transported as chunks from the lower airways of -transgenic mice. Hypertonic saline mobilized a significantly greater amount of mucus that showed a more uniform distribution compared to isotonic saline. Addition of bicarbonate to isotonic saline had no effect on mucus mobilization, but also led to a more uniform mucus layer compared to treatment with isotonic saline alone. mOCT can detect differences in response to mucus mobilizing interventions , and may thus support the development of more effective therapies for patients with muco-obstructive lung diseases.