Disclosed is a hinge assembly for rotatably mounting a trunk lid to a vehicle body. The hinge assembly for a trunk lid of a vehicle, includes a hinge arm configured to be coupled to the trunk lid, a hinge bracket configured to be coupled to a vehicle body and having a hinge shaft, the hinge arm being rotatably coupled to the hinge bracket, a torsion bar configured to be coupled to the hinge arm and to provide an elastic force to the hinge arm in an opening direction, and a cushion assembly provided at one end of the hinge arm adjacent to the hinge shaft and configured to adjust a rotation speed of the hinge arm in response to the elastic force of the torsion bar.