[Pt15(CO)30]2- was synthesized by reductive carbonylation of H2PtCl6 in the channels of FSM-16 modified with NEt4Cl. The platinum clusters in the channels whose diameter was 28 Å were characterized by Pt LIII edge EXAFS as well as FT-IR. UV-vis spectroscopy, and TEM measurements. After exposure of H2PtCl6/NEt4Cl/FSM-16 to CO + H2O at 323 K, Pt carbonyl clusters were selectively produced. The Pi LIII edge EXAFS spectrum of this sample was exactly the same as that of [NEt4]2[Pt15(CO)30], and gave Pt-Pt distances typical of these types of platinum clusters at 2.68 and 3.08 Å. Uniform platinum "particles" (15 Å diameter) were observed in the channels of FSM-16 by a TEM measurement ; this suggests that [Pt15(CO)30]2- was synthesized in the channel of FSM-16. The platinum clusters in the channel were converted to platinum metal particles by evacuation above 363 K. Pt LIII EXAFS spectra of these samples revealed that the bridge CO of the clusters were desorbed by the evacuation at 343 K while retaining their cluster framework ; the clusters were converted to Pt50-60 particles by evacuation above 363 K.