An organic monolayer with a thiol group at its end was formed on a hydrogen-terminated (H-) Si(111) surface via Si-C covalent bond by hydrosilylation. PtCl42- complex ions were then immobilized on the thiol-terminated monolayer by immersing the substrate in an aqueous solution of K2PtCl4 using a strong interaction between the Pt complex and thiol groups. The immobilized Pt complexes were then reduced to Pt nanocluster by NaBH4. Precise surface structure was characterized and it is proven that Pt species were indeed deposited only on top of the thiol-terminated monolayer.