Pt and Rh nanowires and/or particles were prepared in mesopores of FSM-16, and their characterization and catalytic performances were investigated. Irradiation of UV-Vis light to FSM-16 (pore size 2.7 nm) impregnated with H2PtCl6 in the presence of water and 2-propanol (or methanol) vapors led to the formation of Pt nanowires (diameter 2.5 nm, length 50-300 nm) in the mesopores of FSM-16. In contrast, H2-reduction of H2PtCl6/FSM-16 at 673 K for 2 h resulted in the formation of Pt nanoparticles in FSM-16. The XANES and XPS studies show that the Pt wires and particles are slightly electron-deficient, implying the interaction with the internal surface of mesopore. At the initial stage of the formation of Pt wires, it is found that small Pt nanoparticles are formed in the mesopores. Then Pt ions migrate and are reduced on the surface of the small particles, thus resulting in the formation of the Pt nanowires. Rh nanoparticles were prepared in FSM-16 by calcination of RhCl3/FSM-16 at 673 K and subsequent H2-reduction at 473 K. Furthermore, nanowires (diameter 2.5 nm, length 10-50 nm) were formed in FSM-16 by the similar photoreduction of the FSM-16 co-impregnated with H2PtCl6 and RhCl3. In hydrogenolysis of butane, Pt nanowire/FSM-16 exhibits higher catalytic activities than Pt nanoparticle/FSM-16, while Pt-Rh nanowire/FSM-16 shows high activity of isomerization to isobutane. © 2001 Elsevier Science B.V. All rights reserved.