The structure of a nonlinear magnetosonic wave in a multiple-ion-species plasma is analytically investigated, and the elemental composition of ions reflected by the magnetosonic wave is studied. Firstly, stationary solutions of magnetosonic waves propagating perpendicularly to a magnetic field in a plasma consisting of electrons and two-species ions are obtained from a fluid model. Secondly, on the basis of the solitary wave solution, conditions for ion reflection are discussed. Then, the fraction of high-energy ions produced by a magnetosonic wave is expressed in terms of the ion mass, charge, thermal speed, Alfven speed, and wave amplitude. It rapidly decreases with increasing mass. It is found that most of the light ions can be reflected in a multiple-ion-species plasma even for small-amplitude waves if the masses of the main component ions are sufficiently heavy. (author).