Rare-earth disilicide nanowires grown on vicinal Si( 100) with a miscut of 2 - 2.5 degrees toward the  azimuth at 600 degrees C were studied by scanning tunneling microscopy and compared with those grown on flat Si( 001). In contrast to rare-earth disilicide nanowires grown on flat Si( 100) surfaces, the nanowires grow unidirectionally along the [ 011] direction of the vicinal Si( 100) surface. Rare-earth disilicide nanowires form bundles composed of single nanowire units on both flat and vicinal surfaces. Yet, on the vicinal surface, the bundle width is comparable to the width of the terrace. The average nanowire length on the vicinal substrate is longer than that on the flat substrate. Scanning tunneling spectroscopy shows that the rare-earth disilicide nanowires have metallic properties.