Abstract: Mortise-tenon joints, the weakest links in ancient timber structures, are more vulnerable to disruption than members, and thus are crucial to preventive strengthening of the whole structure. In order to improve the seismic performance of mortise-tenon joints, a type of displacement amplification friction damper was designed. A full-scale one-way straight mortise-tenon joint without dampers and three counterparts with dampers were fabricated and subjected to pseudo-static testing. Failure modes, moment-rotation relationship, skeleton curves, strength degradation curves, stiffness degradation curves and energy dissipation capacity of both the strengthened and un-strengthened joints were obtained and analyzed. The displacement amplification effect and tenon-pulling inhibition capacity were analyzed. Results show that the bending capacity of the strengthened joints is 2.3 times larger than the unreinforced one. The maximum rotation angle of the damper is enlarged by 4.5 times compared with the mortise-tenon joint. The hysteretic energy dissipation capacity of the mortise-tenon joint is greatly improved without significantly increasing the stiffness, and the improvement degree gets larger with higher bolt pretension. With the increase of bolt pretension, the maximum energy dissipation can be increased by 3.9 times. The damper can effectively restrain the pulling out of tenon, and the inhibition effect is more significant with the increasing of bolt pretension strain. The research results can provide technical reference for the scientific strengthening of ancient timber structures.