An axle assembly for a driving wheel of a vehicle allows a wheel-side joint and a shaft to be rotated separately from a boot while driving so as to prevent generation of friction noise of the boot. The axle assembly includes the shaft rotated by receiving driving force from a powertrain; an axle housing disposed to pass through a center of a steering knuckle connected to a steering apparatus; a wheel bearing mounted between the steering knuckle and the axle housing; a joint bearing mounted on an outer part of the shaft; and a boot unit configured to have a first end coupled to an outer race of the joint bearing and a second end coupled to an outer race of the wheel bearing so as to form a space filled with a lubricant outside the shaft.