In recent years, one-dimensional silicon nanowires (SiNWs) have attracted much attention of research due to their potential application in nanoscience and nanotechnology. SiNWs are expected to play an importance role in nano-electronics and optical devices. Many synthesis methods, including laser ablation and thermal evaporation have been developed and studied intensively in order to obtain SiNWs in large scale. In contrast, the modification of SiNWs has not been taken much attention. This thesis focuses on the modification and the characterization of SiNWs by various techniques. To enhance the stability and improve the optical properties, SiNWs were treated by ammonia vapor decomposed in a hot filament chemical vapor deposition (HFCVD). The structure changes due to the treatment were characterized by Raman and FT-IR spectroscopies as well as Scanning Electron Microscopy (SEM). The observed N related vibration modes in FT-IR characterization of the treated SiNWs indicate that the surface of the SiNWs have been nitridated. Highly efficient and stable photoluminescence (PL) has been observed from the treated SiNWs at the room temperature. The PL intensity was found to be enhanced several times after the treatment without any luminescent decay. The PL characteristic peak generally contains a multi-peak feature, composing the PLs from the core of SiNWs and silicon suboxide in the Si-SiO interface. The PL characteristic peak shifts from low wavelength (580 ~ 800 nm) to higher wavelength (800 ~ 950 nm) when the treatment temperature increase from 600 0C to 700 0C, indicating the conversion of SiNWs into silicon oxide due to the thermal oxidation and bombardment at high temperature. Furthermore, SiNWs was modified by coating with Au. The modification is expected to provide good contact of SiNW surface with electrode in device fabrication. Interestingly, when SiNWs coated with Au were annealed in furnace at 10-2 Torr pressure and at about 800 0C without carrier gas, uniform and very thin AuNWs were found inside the cores of SiNWs. Transmission electron microscopy (TEM) images indicated that the AuNWs formed are of diameter about 10 nm and length up to 1 micrometer. Under high resolution TEM, the lattice fringes with an interlayer spacing of about 0.235 nm which corresponds to the spacing in Au crystal were observed, indicating that the AuNWs are well crystalline.