The filling of platinum within mesoporous silicon prepared in highly doped p-type silicon was investigated. The deposition of platinum within the mesopores was achieved when using a solution with Pt (II), while the pores were kept empty in a solution with Pt (IV). The particles of platinum were obtained by displacement deposition. The particles were distributed uniformly within the mesopores. The electrodeposition under a weak cathodic polarization resulted in the formation of platinum rods due to the continuous filling from the bottom. The displacement deposition was successfully suppressed by modifying the pore wall by an organic group. The amount of platinum deposition obtained under the cathodic polarization was significantly decreased when using the wall-modified mesoporous silicon. These results suggest that the electrodeposition and displacement deposition occur simultaneously within as-prepared mesoporous silicon.