A fixing device of a nasogastric tube contains: an adhesion member, a connection member, and a retainer. The adhesion member includes an adhesive face, a circular column, and an engagement portion. The connection member includes a connecting sheet, a locating post, and a spherical portion. The connecting sheet has a rectangular slot and an annular orifice, such that the annular orifice accommodates the engagement portion of the adhesion member, the rectangular slot slidably receives the circular column of the adhesion member, an end of the connecting sheet proximate to the annular orifice is connected with the locating post, and the other end of the locating post is connected with the spherical portion. The retainer includes a coupling bar and a joining knob. The retainer further includes a clamp section and two press portions. Furthermore, the clamp section has a hollowly circular space defined therein.