An ultrathin endoscope auxiliary system includes an overtube (110) and a mouth piece (150). The overtube (110), which allows the ultrathin endoscope (160) to be inserted therein, includes a transparent cap (112), a side opening (114), a deflecting member (180) and a positioning member (120). The transparent cap (112) is disposed at the front end of the overtube (110)； the side opening (114) is disposed on the overtube (110) and approximates to the front end of the overtube (110)； whereas the deflecting member (180) is disposed within the overtube (110) and the positioning member (120) is disposed outside the overtube (110) and approximates to the side opening (114). The deflecting member (180) is capable of deflecting the ultrathin endoscope and thereby allows the ultrathin endoscope (160) to be extended outside the overtube (110) through the side opening (114). The mouth piece (150) works with the overtube (110) to adjust the length and the axial orientation of the overtube (110) in the subject.
