To provide a bicycle hub unit and a bicycle wheel assembly that allow a wheel unit to be appropriately coupled to a hub body, a bicycle hub unit is coupled to a rotary body to which a brake is applied by a brake device. The bicycle hub unit includes a hub body that rotates around a hub axle and a rotary body coupling portion that couples the rotary body to the hub body. The hub body includes a first joint portion and a second joint portion. The first joint portion includes an external thread coupled to an internal thread of the wheel unit. The second joint portion is coupled to a restriction member that restricts relative rotation of the first joint portion and the wheel unit.