Abstract
The propgation of an ion-acoustic soliton through a mass interface of cold ions in a plasma is investigated both for a discontinuous change and for a gradual change. It is shown that the behaviors of transmitted waves are similar for both cases and an incident soliton may fission when it passes through the mass interface from the region of heavy ions to that of lighter ones. It is also found that the plane of density discontinuity moves towards the propagation direction of the incident soliton after its passing.