There is provided a mixture ratio stabilizer for a liquid propellant rocket engine which comprises: a body internally having a chamber and a fuel supply hole communicating with an end of the chamber to receive fuel from a fuel supply pump, an oxidizer inlet, and a fuel outlet; a spool guide in the chamber and including a plurality of first orifices for the fuel outlet and the fuel supply hole to communicate with each other; a bellows in the chamber and having one end adjacent to the spool guide and the other end positioned adjacent to the oxidizer inlet, to expand and contract in accordance with the pressure of an oxidizer which flows into the oxidizer inlet; and a spool having a part placed in the spool guide.