Objectives and methods: Fifty normal pregnant women ranging from 26 to 41 weeks of gestation underwent ultrasonographic examination. First, we identified the trachea between both bilateral carotid arteries in the cross-section of the fetal neck. We then traced the trachea up to the bilateral bronchi, observed the spatial correlation to the heart and great vessels, and clarified the optimal section for identifying the respiratory tract image. Last, we measured the inside diameters of the trachea and bronchi. Results: The fetal respiratory tract could be identified below the larynx. In the three-vessel tracheal view, the cross-sectional image of the trachea was most easily seen behind the middle portion of the transverse aorta. When the aortic arch was clearly depicted, the cross-sectional image of the left bronchus was confirmed slightly occipito-posteriorly to the right pulmonary artery and inside the arch. In addition, bifurcation of the tracheae and bilateral bronchi were easily described by tracing the left bronchus medially. The ductal arterial arch view provided a cross-sectional image of the left bronchus between the right pulmonary artery and the ductal artery. Further, several other standard views obtained in cardiac screening also provided distinct images of the respiratory tract. The azygos vein was the landmark of the right bronchus. The fetal trachea and bronchi were measurable after the 26th week of gestation. Average inside diameters of the trachea and the right and left bronchi increased gradually from 2.9 mm, 2.0 mm, and 1.9 mm, respectively, at 26-27 weeks to 6.0 mm, 4.7 mm, and 4.6 mm, respectively, at 40-41 weeks of gestation. After week 36, the inside diameters of the trachea, and the right and left bronchi exceeded 4.5 mm and 3.0 mm, respectively, in all cases. Conclusion: The fetal respiratory tract can be observed concurrently with the cardiac screening examination of the fetus. This makes prenatal screening of pathologic condition of the fetal respiratory tract possible.