In the post-orogenic phase of a mountain's life history, erosion is the dominant process shaping the landscape and elevations. As the highland is eroded away, a broad regional isostatic rebound occurs and the base of the mountain is uplifted and rivers cut down in response to new base levels. Absolute elevations of the highland decreases with time. This erosion-rebound process can be quantified as the unloading of a lithospheric plate overlying a fluid mantle. The adopted rheological model is a viscoelastic plate characterized by an effective flexural rigidity and relaxation time constant. The rate of erosion is assumed to be proportional to the elevation at any time. The erosion-rebound model has been applied to the southern highlands of Australia. It is consistent with recent geological estimates of Tertiary erosion rates.