A simple binary-solvent model is theoretically employed to study the size-effect on selective solvation. We consider multi-component hard-sphere molecules with solute-solvent attraction. We employ the PY approximation to calculate coordination numbers. The calculated coordination number shows that the solute attracts more large solvent molecules than small solvent molecules at a weak attraction. The solute, however, attracts small solvent molecules at strong attraction. To study the selectivity, we divide the size-effect into the exclude effect and the steric hindrance. Attractive strength increases the steric hindrance of large solvent molecules more than that of the small solvent molecules. (C) 2003 Elsevier Science B.V. All rights reserved.