A hinge assembly includes a pivotal shaft, a connecting member, a supporting member, a stationary member having an engaging surface, a rotating member having a receiving surface, and a locking member. A first end of the pivotal shaft is fixed to the connecting member. A second of the pivotal shaft is passed through the supporting member, the stationary member, the rotating member, and the locking member. The stationary member is fixed on the supporting member and is rotatable relative to the pivotal shaft. The rotating member is non-rotatable relative to the pivotal shaft. The engaging surface forms two first positioning protrusions and two second positioning protrusions. The receiving surface defines two first positioning grooves to receive the first positioning protrusions and two second positioning grooves to receive the second positioning protrusions. A height of each second positioning protrusion is larger than a height of each first positioning protrusion.