A method of videothoracoscopy-assisted extended thymectomy procedure performed through a movable small access window is introduced. The access window can be moved stepwise and longitudinally alongside full sternotomy to be upon the dissection site. The majority of the thymectomy procedure can be directly viewed and operated from the moving window. However, partial and complete thoracoscopic maneuvers are required for dissection of the lateral-most region near the phrenic nerve and the upper poles of the thymus, respectively.