To provide a bearing unit for wheel enhanced in reliability by increasing and stabilizing the slip torque of a hub bolt while reducing the size and weight of the unit.

In this bearing unit for wheel including a bolt insert hole 6a bored in a wheel mounting flange 6, and a hub bolt 7 with a serration 7a formed at a neck part, which is press-fitted to the bolt insert hole 6a, the axial length A of the serration 7a is set longer than the length B of the cylindrical part of the bolt insert hole 5a, and a front-side serration 7a1 is protruded from the flange side surface to the press-fitting direction of the hub bolt 7. Therefore, even if the tooth surface of the front-side serration 7a1 where the contact surface pressure is increased is shaven off to break the shape in the process of press-fitting the hub bolt 7 to the bolt insert hole 6a, the slip torque of the hub bolt 7 is effectively increased and stabilized without being influenced thereby.