We investigated the formation of Pt silicide nanowires on a Si(100) surface using scanning tunnelling microscopy and high-resolution photoemission spectroscopy. Pt silicide nanowires with a tetragonal Pt2Si structure are formed along the step edges of Si(100). Pt-induced c(4 x 2) reconstructions also appear adjacent to the tetragonal Pt2Si nanowires. Formation of the Pt2Si nanowires is attributed to the anisotropic lattice mismatches between the tetragonal Pt2Si structure and Si(100). Scanning tunnelling spectroscopy data show that the nanowires are metallic. The stoichiometry of Pt silicide is confirmed by high-resolution photoemission spectroscopy.