A hinge assembly includes a housing, an arm and at least one spring. A damping device includes a damper having a piston rod, a maintaining member secured in the housing and an adjustment member. The adjustment member is movably connected to the maintaining member and has a protruded portion located corresponding to the piston rod of the damper. When the adjustment member is moved to a first position relative to the maintaining member, the protruded portion of the adjustment member is located toward the piston rod of the damper, so that the piston rod contacts the protruded portion and retracts to perform damping function. When the adjustment member is moved to a second position relative to the maintaining member, the protruded portion of the adjustment member is moved away from the piston rod of the damper, and no damping function is available.