The present invention relates to a self-locking bolt-nut assembly including a bolt; a nut tightened on the bolt; and a washer provided between the bolt and the nut, wherein the nut has a counterbore being formed in the nut, and has a plurality of stop protrusions formed on the inner surface of the circumferential sidewall of the counterbored portion of the nut, the stop protrusions being arranged in a circumferential direction at regular intervals, the washer including the rotation-preventive protrusion protruded on inner circumference of the washer towards the center thereof, the rotation-preventive protrusion being inserted into the insertion guide groove; and a plurality of elastic protrusions which is protruded on outer circumference of the washer, being inclined in the direction where the nut is turned to tighten it.