In this paper, we report a kind of novel belt-like nanostructure of iron silicide, which we call nanobars, synthesized on silicon (001) substrate by microwave plasma method. The iron silicide nanobars were found to be of metallic α-FeSi2 with tetragonal symmetry (a=b=0.2695nm and c=0.5390nm) by energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The scanning electron microscope (SEM) morphology indicates that the nanobars, with lengths typically up to several micrometres, widths in the range of 20-200 nm and thickness of 10-100 nm, self-assembly align along <110> directions on (001) silicon substrate and form network structure. The possible self-assembly growth mechanism of iron silicide nanobars was discussed. It is suggested that the optimal matching directions, the reconstruction in high temperature, and the interaction between original depositional iron nanoparticles by the magnetization of microwave magnetic field are the three factors that caused the formation and orientation of iron silicide nanobars. The special structure and self-assembly growth mechanism of iron silicide nanobars might be used in MEMS and NEMS fabricating or self-assembling carbon nanotubes integrated nanocircuits from the bottom up.