Hemimegalencephaly is a rare neuronal migration disorder that can be defined as abnormal neural and glial proliferation localized to all or part of a cerebral hemisphere. Most patients demonstrate intractable epilepsy, with early onset before 1 year of age. Surgical resection is one of the treatment options. In recent years, many advanced intraoperative techniques have been used for brain surgery for various pathologies. Intraoperative ultrasonography is a time-saving and noninvasive method for intraoperative imaging. In this report, we present the use of intraoperative ultrasonography in a patient with focal megalencephaly as an anatomical navigation with the functional navigation system, electrocorticography. In this report, we present the use of intraoperative ultrasonography in a patient with focal megalencephaly as an anatomical navigation with the functional navigation system, electrocorticography.