The present invention relates to a medical chair backrest sliding structure and, more specifically, to a medical chair backrest sliding structure, which allows a sensitive procedure such as plastic surgery to be carried out stably by enabling the backrest to move, when adjusting the angle of a backrest, in the vertical direction, in a state in which the backrest makes contact with the back of a patient, such that even if the angle of the backrest is adjusted the movement of the patient is prevented. To achieve the above mentioned objective, the present invention relates to the medical chair backrest sliding structure comprising: a backrest hinge-coupled with a seat plate； a chair leg-portion provided to a lower part of the seat plate； and an angle adjustment portion for adjusting the angle of the backrest, wherein the back part of the backrest comprises a backrest frame hinge-coupled to the seat plate, the backrest moves vertically along the backrest frame, the backrest frame includes one pair of LM guides, and an LM block, which moves along the LM guides, is provided on a rear surface of the backrest.
