This study aimed to compare the effects of wearing and not wearing a baby carrier on diaphragm movement, thoracic mobility, and forced vital capacity (FVC). A baby carrier is a device used to hold a baby weighing about 3 to 8 kg or more for at least 6 months before it starts moving on its own or during the parenting period. Wearing a baby carrier for a long time increases pressure on the shoulders, chest, and abdomen, causing muscle fatigue. The current study comprised a cross-sectional design and randomized controlled trial including 20 healthy adult males between the ages of 19 and 29 attending the University in Chungnam. An ultrasound was used to measure diaphragm movement, while a tape measure was used to measure thoracic mobility before and after wearing a baby carrier. In addition, the FVC was measured using a spirometer. Diaphragm movement, thoracic mobility, and FVC were significantly decreased after wearing the baby carrier. These results suggest that wearing a baby carrier can negatively affect thoracic mobility, diaphragm movement, and FVC in healthy adult males.