Maoto, a traditional Japanese Kampo medicine, has been used to treat various respiratory diseases, including respiratory infections and influenza. Ephedrine (EPD), the main ingredient in maoto, is also clinically used to treat respiratory diseases. However, the pharmacokinetics and distribution of EPD in the lungs after the administration of maoto have not been demonstrated. This study aimed to determine the concentrations, distribution, and pharmacokinetics of EPD and its precursor methylephedrine (MEPD) in the lungs of rats orally administered maoto (1 and 4 g/kg). We used liquid chromatography-electrospray ionization-tandem mass spectrometry to measure the ingredient concentrations. Both ingredients were detected in maoto-treated lung homogenates. Next, we examined the distribution of both ingredients in lung sections by using matrix-assisted laser desorption/ionization-mass spectrometry imaging, a powerful tool for the visualization of the distribution of biological molecules. The mass spectrometry imaging analysis detected only EPD and provided the first visual demonstration that EPD is distributed in the alveoli, bronchi, and bronchioles in the lungs of rats orally administered maoto (4 g/kg, three times at 2-h intervals). These results suggest that the pharmacological efficacy of maoto for the amelioration of respiratory symptoms is related to the distribution of EPD in the lung.