A machining toolholder including a body, a horn and a piezoelectric actuator is disclosed. The body includes a center through hole extending in the axial direction therein. The center through hole includes a first hole section and a second hole section. The horn includes a first section and a second section which are disposed coaxially and connected with each other. Part of the first section is slidably inserted into the first hole section. The second section is connected to the body and engaged with a tool. Part of the surface of the second section contacts with a wall surface of the second hole section. The piezoelectric actuator fits around the horn and is controllable to drive the tool to vibrate. With this design, the machining toolholder could have good stiffness and connection stability, and could resist to the stress effectively.