Video-assisted thoracoscopic surgery for pediatric patients has gained popularity due to better outcomes than open surgery. For this procedure, one-lung ventilation may be necessary to provide an adequate surgical field. Confirming lung isolation is crucial when one-lung ventilation is required. Recently, we experienced a case in which one-lung ventilation was confirmed by ultrasonography using the lung sliding sign and the lung pulse in an infant. Since lung ultrasonography can be performed easily and quickly, it may be a useful method to confirm lung isolation, particularly in emergency surgeries with limited time, devices, and experienced anesthesiologists.