BACKGROUND AND PURPOSE: Assisted Autogenic Drainage (AAD) is suggested as a promising technique for effective secretion removal, especially in non-cooperative patients, including infants. However, there is a scarcity regarding the effects of AAD on diaphragmatic function. This study aimed to evaluate the immediate effect of the AAD technique on diaphragmatic function in a healthy infant. METHODS: Case Presentation-This exploratory case study involved a healthy 1-year-and-2-month-old female infant. CARE case reporting guidelines were followed. After collecting demographic data, the AAD technique was applied for 5 min using an abdominal belt. Diaphragmatic function, including excursion (DE) and contraction velocity (CV), was assessed via ultrasonography before and after the intervention. RESULTS: Post-intervention, significant increases in inspiratory DE (12.08-18.57 mm), expiratory DE (9.28-16.33 mm), and CV (17.14 to 27.65 mm/s) were noted, indicating that AAD positively impacts diaphragmatic function. These results reflect a notable improvement in diaphragmatic mobility. DISCUSSION: With regard to the potential mechanism, the increased diaphragmatic excursion observed may be attributed to a temporary enhancement of thoracoabdominal synchrony. The abdominal belt utilized during the intervention likely provided stability to the abdominal muscles and the zone of apposition of the diaphragm. Further studies are needed to investigate how long these effects persist.