A fixing device is applied to fix a breathing tube which includes a free segment located outside a patient, and the fixing device contains: an adjustable collar, a connector, and a fixer. The adjustable collar surrounds a limb of the patient, and the adjustable collar includes a first part and a second part opposite to the first part. The connector connects with the adjustable collar, wherein the first part and the second part of the adjustable collar respectively insert through the connector. The fixer includes a base mounted on the connector and includes two arms extending outwardly from the base so that the free segment of the breathing tube is clamped by the two arms.
