During surgery of the middle ear, the presence of disease in the tympanic sinus is very difficult to be assessed. The authors observed the tympanic sinuses of cadaver ears with the nasal endoscope of 2.7 mm diameter and 70 degree angle and evaluated the possibility of endoscopic assessment of the tympanic sinus. Using this endoscope, the landmarks such as the pyramidal eminence, the styloid eminence, chordal eminence, subiculum and ponticulus, and four sinuses such as sinus tympani, lateral tympanic sinus, posterior tympanic sinus and facial sinus of the posterior tympanum could be clearly visible and well evaluated. We present the endoscopic images and benefits of the endoscopic evaluation of the tympanic sinus.