Disclosed herein is an ultrathin endoscope auxiliary system and its uses thereof. The auxiliary system includes an overtube and a mouth piece. The overtube, which allows the ultrathin endoscope to be inserted therein, includes a transparent cover, a side opening, a deflecting member and a positioning member. The transparent cover is disposed at the front end of the overtube the side opening is disposed on the overtube and approximates to the front end of the overtube the deflecting member is disposed within the overtube and the positioning member is deposed outside the overtube and approximates to the side opening. The deflecting member is capable of deflecting the ultrathin endoscope and thereby allowing the ultrathin endoscope to be extended outside the overtube through the side opening. The mouth piece works with the overtube to adjust the length and the orientation of the overtube in the subject.在此揭示一種細徑內視鏡用的輔助系統及其用途。所述輔助系統包括一外套管和一口咬固定器。所述外套管可令細徑內視鏡穿設其中,且包括一透明觀察蓋、一側孔、一轉向件和一固定件。所述透明觀察蓋設於外套管的前端,側孔設於外套管之一側且靠近所述前端,轉向件設在外套管之內部,固定件則設於該外套管外部並靠近該側孔。所述轉向件可使穿設於外套管內的細徑內視鏡由側孔伸出至外套管外部。所述口咬固定器則可與外套管協同作用,以調整及固定外套管於個體體內之長度及軸向。100‧‧‧輔助系統110‧‧‧外套管112‧‧‧透明觀察蓋114‧‧‧側孔120‧‧‧固定件150‧‧‧口咬固定器180‧‧‧轉向件