A pierce nut used for a high-strength steel plate according to the invention includes a female screw thread portion formed in the center of a nut body, an annular piercing portion projecting around the female thread portion, and an annular outer peripheral projection extending from the periphery of the nut body. The outer periphery of the piercing portion forms a first sloping surface increasing in diameter toward the leading end thereof, and also the inner peripheral surface of the outer peripheral projection forms a second sloping surface increasing in diameter toward the leading end thereof. Serrations are formed on the second sloping surface. Even where a mating member is a high-strength steel plate, the pierce nut according to the invention can ensure the same peeling strength and rotation torque as with a conventional nut, without deformation of the pierce nut itself.